Develop a Mobile Voip Software

I want to get develop a mobile application for platform Android, Ios and windows. which works on SIP protocol and used for making VoIP call using an internet. I want to get technology so this this application will work on internet where even SIP is blocked. as thus application will be used for making VoIP call in other country where internet operator don't allow it work in standard codes. Voip service providers use this application to offer VoIP services. this application is get instigated with softswitch. so that user name of this softswitch used to make calls by this application.