Very bad reception
I had three for about 4 months then had to switch to Vodafone as the reception was just awful in rural areas as well as in central London. They claim they have best 3G coverage, which may even be true, but they don't mention that they have the worst mobile coverage! If you have connection, it is often 3G, but a lot of the time you just don't have any connection at all! Vodafone at least gives me stable G connection so I can make calls.