3 have improved a lot over the last few years and now is the time to join them, back in 2003 to 2006 the network was still new and under construction.
Remember how bad Mercury One2One was? It didn't cover outside London until around 1997 and even then it was still bad, so that means it was not possible to get a signal outside London for nearly 4 years after launch! By 2000 the network coverage was average and in basement flats and rural places as well as nightclubs, it was still crap. 2005, the same and 2010 they merged there 3G infrastructure with 3's and it is slightly better, even when you have decent 3G coverage the internet from T-Mobile is slower than 3 even though its same network.
And remember when Orange started(Built by the people who bring you 3 today), it wasn't that good until around 1998 when its network coverage expanded massively.
And then there is NTL Digital Cable, they should have completed there analogue upgrades by 2005, its now 2010 and still there are two/three major franchises still Analogue.
So sometimes you just need to give things time to roll out as it cannot be done overnight. and then you have people moaning about masts going up which also causes delay!