Flutter ASTPP Dialer App

I would like a single Flutter code-base that compiles cleanly for both iOS and Android and functions as a soft-phone for my ASTPP switch. The primary workflow is “calling-card” style: • A new user opens the app, authenticates once via their phone number (SMS or OTP)... (Budget: $250 - $750 USD, Jobs: Android, Android App Development, Dart, Flutter, iOS Development, Mobile App Development, Mobile Development, SIP, Stripe, VoIP)