[Asterisk-Users] Automatic Codec change for different communication channels!?

[Kib Eki]

Hi,

I am looking for a way to let * choose the voice codec relying to the 
used communication channel.

Example
I am using a Polycom 500 which supports G729 and G.711.
When I am doing internal calls (with my LAN) or calls over the PSTN 
(ISDN) I want to use the G.711 codec because there is enough bandwith.
When I am doing inter asterisk calls (over my WAN to another * server) I 
want to use G.729.

Is there a way how i can achieve this?

Kib