Asterisk 1.8+FreePBX 2.11 is behind NAT.
Try to connect your phone Cisco SPA303.
Registration takes place.
You can call but cannot hear the voice.
After 30 sec breaks the connection.
Assigned parameters localnet, externip, nat=yes canreinvite=no.
Configured port mapping 5060.
Please tell me what else needs for voice.