We live in a border town in Ontario, sometimes our phone does pick up on AT&T towers and then we cannot receive phone calls or messages. Do US towers end up blocking our service when we are in a border town?
Yes, if your phone is set to switch carriers automatically, the US signal will take precedence if it is the stronger signal. If your plan is prepaid, or roaming is turned off or blocked, this would mean no calls getting through. Most phones have the means to choose your carrier (Koodo) exclusively, and not switch to other, partner, networks. If you provide your phone model, the crew here can let you know how to best adjust your settings.
My wife and I both have the Samsung Galaxy Note 2 and we both have the same problems. We are on a plan. I get unlimited minutes and 1GB and my wife has same minutes and I think 3GB. We have been having problems receiving any calls or SMS messages. We had a friend just tell us she tried to call and it went straight to VM.