O2 is the only provider that still has reasonable plans with global roaming included, if that's important to you. Grab a PAYG SIM card and test out each provid

O2 is the only provider that still has reasonable plans with global roaming included, if that's important to you. Grab a PAYG SIM card and test out each provider's network before you go through the pain of porting. We switched and found the signal to be literally unusable near our house, so we're back on Three. And O2 incorrectly charged us a £200 early termination fee when we switched away. Took a few months of hassling to get that resolved.