The cost/features of contracts on various networks is relatively similar, essentially you're looking at a £30-£35/month contract, usually for 24 months, thatll get you between 500 and unlimited texts, 400-800 minutes, and unlimited data - You should be able to get contracts with O2, Vodafone, and T-mobile at least through CPW with these rough specs and costs.

Edit: There is a 2400mAh battery by Mugen (the standard battery is 1320mAh) however it also comes with a replacement backplate as it makes the device much thicker, and generally horrible. IMO, you'd be far better with an external battery to charge the device as needed when out-and-about, a-la a Powermonkey.