Got a call today from 'O2' saying I was paying £15 per month top up on PAYG. At first they offered me a cheaper deal of £10 per month with 'Simplicity' saving me £5 per month. When I jokingly asked if I could have a free phone too, they told me I could have brand new 'Samsung Wave' for the same price (£10 per month) with 50 free minutes, unlimited texts and free wi-fi, on a 24 month contract. Of course is accepted.
The link doesn't go straight to the deal, but if you search the 'O2' site it's on there.