Went to O2 Store today and they were doing the following offers:
HTC Desire/ Samsung Galaxy S/ Nokia C7
£15 Per Month
100 Mins & Unlimited Text
£10 Per Month
50 Mins & Unlimited Text
HTC HD7 / Nokia N8
£25 Per Month
300 Mins & Unlimited Text
All are on 24 Month Contracts, but you can add £5 extra to make it into a 18 month if you want.
The Desire is also preloaded with 2.2 which is a bonus.
This offer was found at the O2 Worcester store, but I am sure its nationwide.
It also expires on Christmas Eve.