[Freeswitch-users] Presence/BLF

I am trying to get my head around presence/BLF indicators in a mixed endpoint environment. We have a couple Cisco 7940's and a couple Aastra phones (55i and 57i), and some Polycoms (450 and others). Presence works great if I am just using the Aastras, but gets wonky when I mix in other phones. I am using Wireshark to try to understand what's going on, but need some advise on what to look for. Is all this handled with SIP NOTIFY events? Is FS completely in charge of the BLF status on the phones? Thanks for any pointers! -Troy