[UX] Show letters on dialpad for typing phonewords

[hax404]

Hi,

thank you for providing this SIP client for android. I am using linphone on events related to the Chaos Computer Club on the Phone Operation Service (POC).

1. Describe the bug (mandatory)
   For typing in phonewords, like 8463 for TIME, a dialpad which also shows letters is much more convenient than remembering the number itself. Currently I have to switch to the native android dial app to translate the letters to numbers.

I've checked the latest linphone version from both play store and fdroid.

2. To Reproduce (mandatory)
   Look at the dialpad. It does not show letters on the number buttons, like the native android phone app.

3. Expected behavior (mandatory)
   I would like a dialpad with buttons that also show letters, like https://en.wikipedia.org/wiki/Phoneword#/media/File:Telephone-keypad2.svg

4. Please complete the following information (mandatory)

• Device: Google Pixel 6a
• OS: Android 14, GrapheneOS
• Version of the App: 5.2.5
• Version of the SDK: 5.3.47
• Where you did got it from: Play Store, F-Droid

5. SDK logs (mandatory)

6. Adb logcat logs (mandatory if native crash)

7. Screenshots (optional)
   

8. Additional context (optional)

Thank you in advance for improving the dialpad.