Think it depends where you live. i had an O2 contract phone a few years ago but the coverage where I live was rubbish - I could only get a signal at home if I left my phone by the window, so I've gone back to Orange who I've been with for years previously and since. I pay £35 on an 18 month contract and when I signed up they had just taken over Wanadoo broadband. I get 550 mins per month, unlimited landline calls, 200 texts and free broadband for my money which is great. I recently upgraded my phone - keeping the same contract - and got a free I-pod nano 8Gig.
Current offers are Dolphin 35 on an 18 month contract 600 mins unlimited texts with £5 off if you buy online making it £30 per month - but the N95 is not free - but unless you actually want to make video calls I dont rate 3G phones for normal voice calls - you seem to get lots of squiggly noises.