Our ISP is blocking everything except some few things. Even OpenVPN is blocked by them.
Skype, Yahoo and Live Messengers are working in text chat only, they are not connecting through voice.
For iOS devices, Viber and Tango are also working in text mode only.
The only application which is working well is Team Viewer. I connect to the other party's screen, enable voice, and then talk to him. I think that is because Team Viewer uses port 80. This is working only for PCs while other systems don't support team viewer voice chat.
The question is: Is there any voice chat application which uses port 80 for both iPhone and PC?