Don't do it! I was with 3 about 7 years ago and swore to never go back with them.....fast forward to 2011 and I've gone back with them.
I get No signal in buildings, if I do then I get about 3bars but drops out after 10 seconds. If I'm outside I get full coverage however 5/10 ill recieve a message an hour late which is so frigging annoying you have no idea.
Originally they put my problems down to the fact all their masks close to me were broken, these did get fixed but it done fook all to help my signal problems.
If you go to a shop and ask for help with these sort of issues or complain they just say that they can't do anything in store you'll have to ring their help center in india.
Totally useless......... however if you just want to browse the net then its top notch, expect anything else you'll be disappointed.