Build an Android VoIP SIP dialer

VOIP SYSTEMS AG and 007VoIP.com need a basic SIP dialer for Android, keeping in mind these features:
* PREFERED someone that already worked with Dellmont dialers or similar.
* Dialer itself with all the basic functionality of a softphone.
* Call history (calls made by the app itself)
* Address book
* Login/signup activities
* Source code aviability

There is a pre-compiled APK that can be use for further reference and additional resources.

THIS WAS OUR ORIGINAL PROJECT WHICH NEEDS AN UPDATE NOW WITH NEW PROGRAMMING STANDARDS:

We need a basic voip softphone dialer that works with SIP protocol .
dialer has the cummon dialer options like :
- hang
- mute
- speaker
- dial a number
- dial a number from contacts ( phone contact )
- simple call logs saved in the phone database ( Calls , numbers called, call durations , dates )

the code need to be good for future developments . and use the basic principals of clean coding ( Comments , etc ... )

the preferred platform for the application is : Flutter , React-Native
the voip provider only supports the Standard SIP options , not the SIP Over WebSocket .

The Technical skills required :

- ( Flutter / React-Native )
- Mobile Programming
- VoIP Knowledge
- API Calls
- Android Studio

Thank you!