I wrote a push-to-talk program which works fine on emulators. I used
SIP stack before using RTP stack. I register the SIP Server Emulator and
invite the opponent. I started the RTP communication after opponent
accepted the invitation. I also used SDP to describe sound format(AMR),
port and other important things.
But I could'nt try this structure on target devices, because of some
restrictions( SIP Server, lack of FP2 phones,etc..). I decided to use messaging
architecture instead of SIP stack. I sent the phone IP and communication port
via SMS. But no data was reached to opponent. I checked the logs.
What is the problem? I suspect followings:
1-) Phone IP's were not a real IP. They may be behind a DHCP Server.
Their IP's start with 172.X.X.X. I used Turkcell-GPRS to connect internet.
2-) SIP Stack not only describes to communaction data(IP,port,format,etc.. )
but also provides to oppening device ports. There may be a firewall on mobile phones.
3-) GSM operator does not allow all ports. For example, we couldn't access
a webserver using 8090 port. We connected the webserver using 8080 port.

Please help me