Help: Hong Kong Touch Pro in Canada (Cityfone/Roger Wireless)

[8-pointer]

Cutting it short:
Got the Touch Pro for free from Hong Kong, brand new. Sim unlock (as indicated on HTC distributor website w/ IMEI and S/N confirmation).
Flashed to ROM version: 5.07.832.3 Radio version: 1.11.25.01, all from HTC website.
Using the phone in Canada, service provider is Cityfone (the phone indicates Rogers Wireless). I don't have a 3G plan so I'm using regular GSM network.

Problem: Everything on the phone works EXCEPT the phone function itself. Everytime I make a call or receive a call I can only talk for 5 seconds, then the phone mutes automatically.

Tried setting to GSM only and shutting down HSDPA, it just doesn't help at all.

Can anyone identify the problem for me? I really have no clue since I'm new to this pocket pc tech. If HK 3G phone simply doesn't support GSM network in Canada then I don't even do anything with it. If it's just hardware problem then I'd just send it back to HK for replacement.