Switched Iphones and now no service?

Hi, so i recently was given an Iphone 4 from a friend (the exact same kind as my previous one) and I switched the sim card into the new phone and now I get no service. A few times I also got "Invalid Sim" instead. I thought that this was meant to be really easy to switch the Sim card but apperently not. I'm using rogers, if anyone knows an easy fix to this problem that would be greatly appreciated.Id rather not have to drive out to a Rogers store to get this fixed.

Its probably not a rogers iphone and locked to a diff carrier.
get it unlocked.