I recently had my iPhone 4S unlocked by another provider that was on their network and am now using it on the Bell network. If I put it in the My Device section on the mybell.ca site with the IMEI number, can Bell then lock my iPhone making me stuck with a locked phone if I do so?
Only the provider that the phone was originally locked to can re-lock the iPhone. Putting the IMEI (which Bell already knows if you've used it on their network) into the web form won't re-lock your phone. No need to worry!