The ShoreTel Mobility Routers (aka SMR) is an exciting product that can make fixed/mobile convergence a reality! It builds heavily on inherent SIP functionality in call setup, call flow and Session Description Protocol. It acts as both a SIP client and as a SIP proxy server (e.g. B2BUA). If you are comfortable with SIP protocol, the SMR is a relatively simple device to understand. The products primary contribution to the state of the art is the ShoreTel Roam Anywhere Client (aka SRAC) and the fact that it is available now; it works and there are plenty of reference accounts.