phone is switching carriers on its own?

[NiffiIsenguard]

OK so I'm on bell. And my phone will randomly switch to Telus. I've never seen this happen before. Is it something I should be worried about?
I bought it from Best buy for Bell. It's non branded I belive.

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[SpookDroid]

Do you live near an area with poor Bell coverage? It might be switching automatically because of that. Check your phone bill to see if you have any roaming charges. You can force the phone to stay on one network, but as soon as that network is out of range or with poor signal, your phone won't switch to a better connection.