T-Mobile, Sidekick slide.
Pretty cool phone strong too, i dropped it off my roof by accident onto cement and it still works like new.
I'm using Verizon, hopefully at&t soon ;)
Over here in the United Kingdom we have a service provider called "o2", I would say that they are my favourite so far.
I get some pretty cheap deals and they have a grear customer service.
I use Orange ;) Mainly cause all my mates use it and I get cheaper messaging and calls to other Orange users ;)
Your mom.
Seriously though, I've been using AT&T for 3 years now and have had few problems. Maybe I'm just lucky.
AT&T... haha that's a joke. >_>