[Asterisk-Users] No audio for outgoing calls

[Michaël Gaudette]

Hi,

I've just noticed my Asterisk setup is having a small issue.  

- Whenever I get a call (from VoIP provider to my Asterisk box, forwarded to
my GXP-2000 phone through SIP registration) I get perfectly clear audio,
both ways.

- When I call out with the phone (Phone to asterisk box through SIP
registration, then to VoIP provider, than to PSTN to my home phone) I get NO
audio.

I know the one-way audio can be the fault of firewalls, but this is
different (s I understand it).  What could be causing this breakdown?
Especially since when I get my phone last week, I made sure to call my home
phone and I could hear perfectly.  SO why can cause this sudden problem?
Thanks,

Mike