Tesco Mobile is currently offering the Nokia Lumia 800 for £12.50PM over 24 months, which works out at as (*consults calculator*) £300 total over the two years. Available in black or pink.
The monthly allowance includes 500 minutes, 5,000 texts and 500MB of data.
Tesco Mobile uses the O2 network.
(Thanks to DelBoySmiffy at HUKD)