Why does my iPhone keep telling me I have no service?

Why does my iPhone keep telling me I have no service?

Okay, so I recently bought an iPhone 4 used, but in good condition locked to Telus to replace my broken Samsung Galaxy S4 Mini, also with Telus. The SIM card from my Samsung fits in the iPhone, but when I put it in the iPhone it just keeps saying no service in the corner. I've tried switching carriers from automatic to manual, I've tried restarting the phone, I've tried resetting all network settings, I've even tried restoring the whole phone itself. I do have an account with Telus, and it is still saying no service?!

Could be because you don't have any.

What did they tell you when you called them?

Telus may have to activate the iphone onto the network, I dunno if they still do that but they did years ago before I switched to Wind. Wind for lyfe baby