No voice transmitting on a symbian os based phone over 3G

Hi everybody, this is my first post.
The reason of this is that i have an asterisk pbx at work, it works perfectly on LAN, it also let me connect via internet, but the problem comes when i establish a call from a sip internet client, it rings perfectly and answers perfect, but when the call is on i cant hear voice on the server side ( my LAN), on the remote side (internet side) they can hear me clearly. but not vice-versa, it only works over IAX protocol, but the smart-phones on my office have sip clients(Symbian phones),some people told me that the problems are because the 3G connection isn’t enough faster, i hope you can help me thanks…

Hi and welcome.

Check this out.

Hey, thanks I´ll check it…