There was a bug in certain 3550 and maybe 3750 (not sure) IOS versions which allowed the phones to broadcast to the data vlan for an IP. Do a show cdp neighbor entry * and see if the phone is getting an IP on the correct network.
I don't know if the 6608 has these commands but they worked for me with a 2651 router to an Avaya Definity. These commands are for Wics so I don't know if it will work for you.network-clock-participate wic 0network-clock-select 1 T1 0/0
