I am just coming to the end of my 18 month contract with O2, and decided to have a look to see if i could get a cheaper deal, so after speaking to the staff in the O2 shop, asking what i could get for £20 a month, i was not to chuffed to be told 50 mins (yes 50) and 300 texts. I there fore opted to go with the offer in the new 3 shop, who offered me for the same price, 500 mins and 200 texts. Once signed for, i contacted o2 for my pac code, and amazingly, they could offer me the same deal for the same price!!!!
However, as i had already signed with 3, i decided to stay with them. First day i have tried to use it today, and it has no coverage in my area (work that is), so i have had to go to them and cancel, however, when i rang O2 back, they upgraded my phone, and gave me an option of 300 mins and 300 texts for £15 for 12 month contract. WINNER!!!!

the morale of this tale is, even if you arent planning to leave your network, make them think you are and get free stuff for nowt, that costs you nothing.