recently i've had an issue with my address being used to set up a lot of fraudlent phone accounts. because of this i have had to deal with every mobile company going, my findings so far
O2 (also my current phone provider) UK call centre - fast and brilliant service, basically took the details said don't worry we'll sort from here, and they've been spot on - pleasure to deal with
EE - got through to a UK call centre, again brilliant knew what to do, took details and sorted it, polite friendly super service
Vodaphone - think i was directed to somewhere in asia. people very friendly, but couldn't work out side the script, they didn;t fill me with confidence that the problem was sorted, but to give them their dues, it seems to have been fixed
Orange - se comment for vodaphone
i will tell you what i have found to be the best invention is the new live webchat that O2 use (possilby others) doesn;t matter where they are from or where they are, it just seems to work, typed text is so much easier, no waiting on phones, everything is typed so no mistakes from language barriers. if a company has webchat i use it. i don;t ring unless i really have to.