Mark,

Start looking at the switch port config.

for a ios based switch, with a separate voice and data vlan, your config should be,

int fa0/1

switchport mode dynamic desirable

switchport acesss vlan 100

switchport voice vlan 101

spanning-tree portfast

(excluding any qos configs).

Make sure vlan 101 is able to communicate to the rest of the network.

Also Do you see any duplex, speed errors on the phone port ?

HTH

Sankar

PS: please remember to rate posts!