This deal was posted a week or so ago as a renewal. It's now up on T-Mobile's website, and more importantly, it gets a special rate of cashback (£101+, depending on loyalty bonus) from Topcashback. See http://www.topcashback.co.uk/tmobile/.
Works out at £267 if the cashback tracks. Best price for a sim-free deal, according to Google, is currently £285.
Other phones eligible for the special rate of cashback are
HTC Desire - £20.42 per month
HTC Desire HD - £30.64 per month
HTC Wildfire - 300 mins/300 texts for £15.32 per month
This seems the best offer, though, if you're happy with Windows Phone 7.