Android Apps SIP bridge to GSM Network

Hi, I have a project to develop Android apps to bridge voice from SIP to GSM, below the requirement and flow Requirement 1. Support all Android phone and all android version 2. SIP must support standard sip pbx or sip proxy. example Asterisk or VoipSwitch 3. Option to support SIP TLS 4. Support Wifi and 3G internet apps 1. Android using SIP can register to SIP PBX or SIP proxy using Wifi or 3G 2. SIP PBX/Proxy send call to android phone and android phone will send call to GSM flow 1. SIP PBX/Proxy ->(via internet Wifi or 3G) -> Android Phone -> GSM Network Delivery 1. Deliver the source code and installation apps