Telus/Bell phones do not work on the shared MTS/Rogers network.
Couple Telus owned towers in Brandon, Portage la Prarie, and they work well in Winnipeg, no other GSM access for Telus or Bell customers.
The SpeakOut phones should work fine anywhere on the MTS/Rogers network, but I haven't tested this. Rogers isn't too bad in Manitoba anyways.
Rogers has a roaming agreement with MTS, but not with Telus or Bell.
MTS and Rogers phones will work across the towers fine, Telus and Bell phones are partnered with MTS only for CDMA access, not GSM.
Taking an MTS phone into Alberta would be interesting to see if they will use Telus, Bell, and Rogers' towers, but I suspect only Rogers.
If that was a clear enough explantion, that is how that works.