I bought Nokia 5800 last week on 24 months contract from mobiles.co.uk for £20/pcm + £40 quidco cashback +14 months half price cashback (I don't rely on) - which was a good offer. BUT found a better offer for myself as both of our contracts were due for renewal. I loved the 5800 so went for the same phone - easier with charger and cables when you travel.
This offer is for 24 months £25/pm with O2 i.e. 600 minutes + unlimited text BUT with £200 AUTOMATIC cashback makes it the lowest price for 5800 you can find at the moment £16.27/pm + Quidco £50 ---- BEAT that !!