1. Making a call
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Welcome!
This manual helps you to optimize the usage of the centrexx App (Android), the cloud telephone system by Deutsche Telefon Standard.
We hope you enjoy working with the centrexx App!
Subject to alterations
Version 4 / 01/2026 (EN)
Please find the latest release notes here.
| Type | Icon/Character | Description |
| NOTE
CAUTION
WARNING |  | NOTE: Information that is useful but not critical to the reader.
CAUTION: Tells the reader to proceed with caution.
WARNING: Stronger than CAUTION; means "don't do this" or that this step could be irreversible, e.g., result in permanent data loss. |
| TIP |
| Useful tips that provide additional information. |
| Procedure | 1. 2. 3. | Procedures are numbered steps to perform an action, where the order of the steps is relevant. |
| Result of procedure/action | ⇒ | Indicates the result of an action//procedure. |
| Lists | • • | Used for listings and items where the order of steps is irrelevant. |
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Minimum app/OS requirements
Minimum OS: Android 10
Minimum SDK: 29
Required app version: 2.8.4
Rooted mobile phones will not be supported!
Supported browsers
We recommend the Samsung browser and Google Chrome.
Important
Starting with the Android version 2.8.2, it is required that a browser is installed and enabled on the Android device to allow users to log in. This ensures that all authentication processes work smoothly and securely, regardless of which browser is used.
Login
In order to use the app, you have to login with your centrexx username & password. These are the same credentials you would use on app.deutsche-telefon.de.
Upon first Login, the app will guide you through the settings for
Registration of the mobile number
Permissions requiere for the app to work
Those settings can be changed later on. Please be aware that without the proper permissions the app might not work as intended.
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Giving permissions to the app
When you log into the mobile app for the first time, the app asks you to give access to
Notifications (required)
Microphone (required)
Contacts (local contacts on your device)
Telephone (required)
Camera
Please note that Notifications, Microphone and Telephone are required permissions as they are fundamental to basic functions of the app.
Whilst the other permissions are optional, please note that some features might not work as intended without the corresponding permissions (e.g. you can't make a video call without permitting access to your camera). Please note that you can only change the permissions granted in the Android app settings.
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Registering your mobile phone number
If you would like to receive calls via GSM, you can now register your mobile phone number.
If you want to skip this step for now, you will be able to activate GSM and register your mobile phone number later on in the app's settings.
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Subsequent Login
On subsequent Logins, you can choose to continue a previous session with its settings, delete that session or create a new session.
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Favorites
Once you logged in, the first initial screen is the "Favorites" which match the function keys of your extension.
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General Overview
This view is divided into 5 major sections
The "Favorites" view which can be switched to "Conferences"
A button for quick access of the Dialpad
The Tab Bar to replace 1. with "History" or a "Search" view and back
Quick access to Call Forwarding Profiles and DND
App Settings
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History
The "History" shows a list of recent calls. This view can be switched to "Voicemails" for a view of recent voicemails
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Filter Settings
In the top right corner, below the Quick access to Call Forwarding Profiles and DND, there is a setting to filter the call history by
All
Missed
Accepted
Outgoing
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Search
The "Search" gives you the ability to search for dial targets from the PBX as well as your phones contacts.
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Search options
The search targets are divided into four groups:
Contact: Contacts saved in your PBX
Conference: Available conferences
Group: Call groups in your PBX
This phone: Local contacts on your phone
Search filter
To initiate a search, click on the looking glass in the top right corner. Right below this is a setting to filter the search results by their source like
Contact
Conference
Group
This phone
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Make a call
In order to initiate a call, simply click on any of your favorites, call history or search result. In case you want to dial a specific number, open the dialed via the special button and type the number you want to dial
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Options in a call
The following options are listed in a call.
Mute
GSM
Dialpad
Activate/deactivate speakers
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Receive calls in locked mode
Incoming calls via centrexx can be received like regular calls
While the phone is locked
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Receive calls app is in background
Incoming calls via centrexx can be received like regular calls
While using another app / the app in background
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Receive calls while using the app
Incoming calls via centrexx can be received like regular calls
While using the app
Making an interactive blind transfer
When you are in a call with someone and want to transfer the call to another person without asking the latter if the transfer is possible:
1. Open the advanced call options.
2. Tap the Transfer-button in the options menu.
⇒ The Search window appears.
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3. Type in the name or the number of the contact you want to transfer the call to.
4. Tap on the contact in the search results
5. Tap on Start voice call.
⇒ The call is being transferred to the selected contact. Your call ends immediately.
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What is a dynamic conference call?
A dynamic conference is a conference call that you can start spontaneously by merging calls that are on hold and an active call into one conference call. Once a dynamic conference is started, most options are identical with a planned meeting using meet & share (find more details in the according chapter).
Maximum Participants in a dynamic conference are 8 for the non-premium version of the app and 25 for the premium version.
What are the differences between a dynamic conference and a planned meeting?
While the dynamic conference is spontaneous, a meeting is a conference call that is scheduled in advance, and you have an invitation link that you can share with everyone you want to join the call.
On a dynamic conference, the person who initiated the conference call is the host. On a meeting, the person who scheduled the meeting is the host.
If you join via the web app / desktop app, a meeting starts in video mode while a dynamic conference starts in audio mode. Joining via the mobile app, you always start in audio mode. In any case, you can switch between audio and video mode.
Starting a dynamic conference call
When you are in a call with someone and you want to add another participant:
1. Put the first call on hold and start a second call to the person you want to add to the conference. Or start a second call to another person right away - in this case the first call will be put on hold automatically (consult the chapter Making a call if you are unsure about this step).
2. Tap on the call on hold which is displayed as a bar at the top of your screen.
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3. Tap on Merge all calls to start an ad-hoc conference call.
Note: You could repeat step one and two by putting the second call on hold and call a third participant. Then tap on the bar for Calls on hold and press Merge all calls. In this case it will merge your active call with the two calls you have on hold.
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4. You are now in an ad-hoc conference. Since you have started the conference you are it's host which gives you some additional options which are explained in the next section 4.2.
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4. Call the selected contact. Please note that the first person is put on hold in the meantime.
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5. When the selected contact picks up the call, click on Merge calls to create an ad-hoc conference.
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6. You are now in an ad-hoc conference.
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Options overview for a dynamic conference
Once you have started a dynamic conference as a host you have the following options:
Tap on the options menu (three dots) of yourself.
Tap on the options menu (three dots) of any other participant.
Put the call on hold. Please be aware that this puts the whole conference on hold.
Mute yourself.
Put the conference call on speakers.
End the call.
Please be aware that this would end the conference for all participants since you are the host. If any other participant ends his call the conference woud continue.Open the advanced options including emojis and options exclusice to you as the host.
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Managing the advanced options
If you tap the advanced options button (7 in the options overview above), you have a number of options specific to conference calls or hosting a conference call:
Use emojis like thumps up or applause. They will pop up next to your name and fade away over a few seconds.
Use the raise hand emoji. It will appear next to your name and will disappear only after you tap the emoji again.
Mute all participants of the conference except for you. (host only)
Lock the conference in order to prohibit other participants from joining. As the host you will still be able to invide new participants. (host only)
Transfer the call. Please note that transferring a conference call is usually not recommended. Find more details in the warning below.
Add other participants to the conference. (host only)
In the advanced options you will also find the options to activate your GSM calling or use your Dialpad like in every other call.
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We do not recommend using the transfer option on conference calls. If you do so, the person the call is transferred to will not have the visibility of the conference views nor have access to the conference tools. You can NOT merge two conferences by transferring one conference to another. Do not try! It can lead to unexpected malfunctions since the conferencing system is not designed for it!
When you click on the option menu of a participant (2 in the options overview above), you can:
Mute the participant.
Exclude the participant from the conference. Please be aware that the participant can rejoin the conference unless you also lock the conference in the advanced options (4 in the last paragraph).
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If you tip on the participant options from yourself (1 in the options overview above), you can:
Mute yourself.
Raise your hand (the raise hand option is also available in the advanced options menu).
Leave the conference (this will end the call for all the participants).
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Managing participant's options
In this view, as a host, you can
Mute a member
Exclude a member (this member will no longer be a part of the conference)
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Changing to video mode and gallery view
Like on any other call, you can change to the video mode by tipping the camera button in the upper right-hand corner. While in a conference, the video mode is automatically displayed in gallery view.
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While in video mode, you can:
Tip again on the camera-button in the upper right-hand corner to switch back to audio mode.
Tip on the camera button that has appeared among the options below the gallery to activate or deactivate your camera.
You still have all options described above in the paragraphs Advanced options and Options overview.
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Adding new participants while in a dynamic conference
1. Once you have started a conference, you can use the + button in the upper right-hand corner to add new participants.
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2. A search bar opens. Search your contacts as usual and start a call to the contact you want to add to the conference. Once the call is answered, the new participant automatically joins your conference.
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Does a dynamic conference has a link for joining that I can share?
Yes, it does. But if you start a dynamic conference with your mobile app, you have no visibility of the conference link (like you would on a planned meeting). You have to add new members manually. However, a participant joining via the web or desktop app can access the link and share it with you or other potential participants. This way you can still use an invitation link if you want to invite more people spontaneously.
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To join a meeting, you need an invitation. After you have received an invitation to a meeting, tap on the meeting link to join the meeting. The app will automatically connect you to the meeting.
Joining a Meeting via an Invitation Link
If you have received an invitation link (e.g. by email), tap on the link to join the meeting. The app will automatically connect you to the meeting.
Rejoining a Meeting
To rejoin a meeting in which you have previously participated:
Tap on History in the app menu at the bottom
Tap on a meeting you have joined before
The app will automatically connect you to the meeting.
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Audio Mode
After joining a meeting, you will initially participate in the meeting in the audio mode.
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Using the icons in the bottom bar, you can:
Put the call on hold
Mute/unmute
Activate/deactivate speaker
Leave conference/End call
Access the conference options (up arrow)
Tapping the video icon in the top right corner, you can:
Switch to video mode
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Extended Call Actions
Tap on the up arrow to access the extended call actions. In this menu, as a participant, you can:
Raise/lower hand
Transfer call
Access the dialpad
Switch to GSM
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Extended Call Actions – Host
Tap on the arrow to access the extended call actions. In this menu, as host, you can:
Mute/unmute all
Lock/unlock conference
Lower all hands
Raise/lower hand
Transfer call
Access the dialpad
Switch to GSM
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Host Additional Conference Options
As a host, you see three dots next to participants' names and your own name.
When you click on the three dots next to your name (host), you can:
Mute/unmute yourself
Raise/lower hand
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When you click on the three dots next to a participant's name, you can:
Mute/unmute participant
Exclude participant
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Video Mode
To start the video mode:
Tap on the camera icon at the top right-hand corner
Tap on the camera icon at the bottom left-hand corner. You will have to give the app permission to access your camera.
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In a 1:1 audio call, you also have an option to switch to a video call.
Start video by tapping on the camera icon in the top right-hand corner
Activate camera by tapping on the camera icon in the bottom bar
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Swap Video
Your own video is shown in a small picture in the top right-hand corner, the other participant's video is shown as a full-size picture. Tap on the small picture to swap the videos.
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App Settings
The app settings can be accessed by a click on the user profile in the upper left corner here you can access and change the settings for
"Call With"
"VoIP"
Call Forwarding
Settings
Language
Call Through Number
Register phone number
App Permissions
Furthermore you can end the current session by "Logout" from there.
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Where can you get help?
The information you found in the manual for this product does not answer your question?
We will be happy to help you. If you have technical problems, please open a ticket at service.deutsche-telefon.de - this is the quickest and most efficient way for us to help you.
If you need help immediately, please call us after creating the ticket and give us the ticket number. The technical service can be reached free of charge at the hotline number 0800 5802008.
If you have general questions about our products, e.g. about availability, test positions or similar, please use the contact options given at https://www.deutsche-telefon.de/kontakt.html.