Push to talk with Android

I want to add one feature of Push To Talk kind of application for communication between my Team in my applicatio开发者_Go百科n. Beside this I also need some kind of text messaging. But I want it to be able to work in Gprs.I found that SIP API can be used for making voice calls but it says that it Requires WIFI. I want to make it run on Wifi as well as GPRS.

Can somebody give me some idea where to start from?

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Push To Talk in SIP is just a regular call, with RTP doing the tricky floor control. There's usually a media server involved broadcasting the voice bursts to all participants to save on the scarce upload bandwidth. The server usually has a public address simplifying NAT traversal for participants.

But if you are rolling your own, and don't need interoperability with other SIP services or IMS, and the whole thing resembles instant messaging more than phone calls, XMPP might be a simpler option.

I'm not sure about the Android aspect, but apart from the new, built-in SIP support which might be limited on purpose, there's always the SIP stack from SIPDroid, right?