I've just come off Three, cos the signal was crap & it used to drop out calls randomly to people & to my mates flat (also on Three) less than 400m away.
Currently, I wouldn't go back to Three if you paid me.
Also, be aware that if the 3G signal drops, you're onto T-mobile coverage............
If you have a problem, ALL their call-centres are in India & if you want to talk to someone over here, you can only write to them, they won't take any calls
Or you could rock up at their Head Office in Maidenhead - that kinda gets results
if the 3G functionality is important to you then check it is available in all the places you go to. Around here you will find that a 3G device will fall back to 2G as you move from cell to cell.
I live in SE Wales and found the 3 network was a bit pants. Fine at home in town but gets very patchy once in the Brecon Beacons or Black Mountains. At the time I was working in Hay on Wye so I migrated to Vodafone.