Got this as a DOWNGRADE for my son who wasn't using half of his T-mobile contract but I've been trying it out for a week and I may well give him my next upgrade instead. It's a really nice slider, instant access to Facebook, Live Messenger, Skype, Last.fm, I have all my e-mail accounts 'pushed' to it, (camera is OK (3.2 MP).
In addition to the 300 mins/texts you also get an additional 300 mins of calls to other 3 users (all of the family are now on 3 so this is great). Also plugs into my laptop as a USB Modem.
Best part of the deal is the 6 month contract though! They have another couple of handsets on the same deal (LG KF310 and Nokia 3120).
Quidco offer £32.50 cashback on a new Mix & Match 300 contract and it doesn't seem to specify contract length so worth a try - I already had mine when I noticed that!