If you're going to buy from them, buy from 3 directly rather than a company like Phones4U as these offer deals where you would pay £30 a month, and if it was half price line rental, you have to pay 4 months of £30 then send your bills back to them and they'll give you a cheque for £60. It's very hit and miss, whereas with 3 they'll just charge you the half price to start with.
The Customer Services, well if you're good with technology and fairly smart, then you'll be fine, as you won't need to use them.