pulpoff/gsm2sip ? reverse-engineered prompt

Build me an Android app that turns a rooted phone with a local SIM into a SIP to GSM gateway for an Asterisk server.

I want it to auto answer incoming calls on the SIM, bridge the audio to SIP, and also handle outbound calls when Asterisk sends a SIP invite with an X GSM Forward header and the target number. It should register to my SIP server with a username, password, host, and port, then let me tap Start to bring the gateway online.

Please make it work like a real phone app, set it up as the default dialer, and assume it will run on a Magisk rooted device with the needed permissions and audio tweaks already handled by the module. Use G.722 for good voice quality and fall back to G.711 A law if needed. Include the setup so the APK gets installed through the Magisk module, and if you need anything from current Android or SIP docs, look it up online.