Phones4U are currently doing the Nokia 5800 Xpress in Black/Silver colour on the Orange Dolphin £30pm tariff. It's an 18 month contract automatically discounted by £10pm for the term of the contract, hence £20pm.
I know a very similar deal was posted recently through Dial-a-phone but there was a mixed response regarding their customer service. I've never used Phones4U so cannot vouch for them myself, however I guess at least they have a High Street presence, to help with any issues, etc.
Also I personally think the 5800 looks best in the Black/Silver colour, and I think this colour is exclusive to Orange for some reason?
Oh yeah, £30 quidco cashback available.