Mobile phone - Sim card question

[Xander]

I want to change the sim card in my mobile phone, because my calls are so expensive. You can buy these cards online for about £10 which is cheap, but it says with them:

"NOTE:
Compatible with most mobile phones that are not SIM locked to a specific network."

So, my question is how do I know if my phone is locked to a certain network? Is it as simple as just buying the card and taking mine out and putting it in, would it work straight away?

[Endless]

Ask a friend to do a sim card swap with him to see if your phone's locked. If it is, it'll ask you for an unlock code that you should be able to ask from your phone company providing you've been a customer long enough. Otherwise, you might need tools to unlock the phone.
In the good case, if the other card works straight away in your phone, you know it's not locked.

[Xander]

Thanks, I tried it and it worked! Yay. No unlocking needed =)