the SIP 3.1 Admin Guide list's the supported Audio Codecs on page 4 - 76.
Usually the phone would advertise its codec support withing an Invite to the far end.
Please be aware the SoundPoint IP 601 has been discontinued and is no longer available for purchase. Support for the product will be available until 03/31/2013.
Notice: This community forum is not an official Poly support resource, thus responses from Poly employees, partners, and customers alike are best-effort in attempts to share learned knowledge. If you need immediate and/or official assistance please open a service ticket through your proper support channels. Please also ensure you always check the VoIP , Video Endpoint , Skype for Business , PSTN or RPM FAQ's