do you guys know if giffgaff works on o2 sim locked phone
without ulocking it.
The only problem reported regarding O2 is for Tesco phones.
Tesco is like giffgaff in that it's a virtual network using the O2 infrastructure to give the service.
Tesco mobile lock their phones, and additionally can be locked to O2 - so double locked and difficult to unlock
Pure O2 should be no problem.