asterisk users - Apr 2005 - Grandstream : low bandwidth codec (ilbc doesn't work, any other ? )

Hi,

I'm trying to setup one of free low bandwidth codecs for Grandstream (ilbc, 
g726, ...), but with ilbc I just hear "engine running" in handset.

Is anyone using ilbc sucessfully with Grandstream? Quality ?  Any other 
alternative ?

I use Bristuffed Asterisk....

Thanks in advance,

regards,

Rob.