My mate had the biggest headache trying to cancel his contract when it was close to the end. They wouldn't listen to him and just kept offering him new deals, so I took the phone off him and started shouting at them lol
However their deals seem good which makes up for crap service but think you can only use three sims in three phones, as in you cant chuck the sim into a normal unlocked spare phone as you could do with an o2, vodafone sim.
Edit: This was just before xmas with three.
Haz: I found if you got a tit on the phone to voda customer services, call up and talk to someone else. When I wanted my PAC code, the guy said I'd have to wait a few days for it to come in the post but I needed there and then for a new contract, so I rang up again and the next person gave it to me over the phone.