I'm just glad I've stayed on the Simplicity 20 for iPhone 30 day plan O2 retentions offered me when I came out of contract in Jan.
I pay £19.99 a month for 600 mins and 1200 texts + unlimited data (for now anyway)
I also went down the SIM free iPhone 4 handset purchase route. I've also ordered a free Three PAYG micro-SIM from their website.
O2's tariffs are now quite frankly crap. They have halved the minutes and given you unlimited texts now on all pay 18+24 month contracts. If you now want the same number of minutes you had with the original O2 tariffs, you now have to pay £5 a month more

!
To me O2 seem to be shooting themselves in the foot here somewhat as well. Many many iPhone 3G users came out of contract in Jan this year and O2 retentions offered the 30 day SIM only plan or you could stay on your existing tariff on a month by month basis. Now it's new iPhone time they really don't seem to be doing anything to get these customers back into an 18 or 24 month contract. There's no incentive to sign another contract with O2. Surely that's not a good business model?
I'm also on a monthly plan with my ISP (Plus Net) who regularly try and throw discounts at me to try to get me onto a longer term contract, which I wont do.
I've spoken to O2 customer relations about their new tariffs (along with their poor 3G coverage) and it's another case of 'due to extensive customer feedback....blar blar blar'