The Cisco SPA series is actually great with FreePBX, good quality phones, low cost, actual SIP working on latest firmwares, easy to configure using HTTP or XML.
my favorite model is the SPA514G because it is the only SPA with gig ethernet + PoE.
Also, if you call Cisco for support, they only will support the 7940, 7960 and SPA phones for 3rd party (asterisk) integration.
I also would never recommend a new freepbx rollout with cisco 79xx phones tho!