I want AMR codecs in a call between 2 phones in the same subnet, is that
posible with Asterisk? I got it with a different PBX but I havent got it
with Asterisk yet and I dont know why. The RTP flow is between the
terminals, so why would Asterisk mind about the codec used?

Before the rtp flow is established all the call setup parameters are to be negotiated, the messages in this stage and even when the rtp flow is established directly between two terminals, are exchanged through Asterisk, which is in charge of the call control, so it checks and relays the messages between the terminals and I think it will not accept a call with an unsupported codec, like the amr is .
There is a patch to add the amr support in Asterisk, check .


Marco Bruni