Cisco CallManager officially supports “third-party SIP phones” that follows RFC3261 standard. So, if you have Avaya IP phone, that has standard SIP firmware, it should work (at least to basic SIP functionality). However if your wireless phone is “Dxxxx” model, it works over DECT protocol, and needs DECT base.
Mike / CCNP, CCVP, CCDP, CCSP, etc.
Headset Adapters for Avaya Phones