I think th eip softphone supports
codecs G.711, G.723.1, and G.729A .
To change the codec used to any of this three,
it would have to be negotiated doing capability exchanges
and it would be with respect to the configured region codec.
G.711, G.723.1, and G.729A
Double check the Region and Device Pool configuration in Cisco CallManager, where CODEC is defined.
put the cisco ip phone in the device pool specified for his region.
