I'm currently with fido..and they put me on the 15/50 plan which I like. But my phone is old and I want an sony ericsson phone from Rogers. What do I do? If I buy the rogers phone (Sony Ericsson W580i), do I have to unlock it before I use it with fido? Or do I just switch the SIM card? Again, I prefer to stay with fido but just want the rogers phone.