IIRC voice etc use different ports from the "usual" stuff.
Did you Google the net for the ports? Did you try logging DROPped packets on the fw?
Code:
Feature Outbound Port Inbound Port
Text chatting 80 (TCP) 80 (TCP
Voice– PC to PC 6901 (TCP/UDP) 6901 (TCP/UDP
Voice– PC to Phone 6801 (UDP) 6901 (TCP/UDP
2001-2120 (UDP – dynamic) 6801 (UDP)
6901 (TCP/UDP) 2001-2120 (UDP – dynamic
7801-7825 (TCP – dynamic
File Transfer 6891-6900 (TCP – dynamic) 6891-6900 (TCP – dynamic)
MSN Messenger Service 1863 (TCP) 80 (TCP)80 (TCP)