Ok, I just read about last 15-20 pages of this thread, probably barely caught up with the end of it as new posts keep being added (and there'll probably be 20 new ones by the time I manage to post this).
My question:
I'm with O2 and have 7 months left on my contract, so 7x£20=£140 to buy myself out of the contract, and start a new contract.
But, I was wondering, could I buy a new phone from Apple, SIM-free, then ask for a micro-sim (or even cut my existing one), and continue my current contract, until it expires, using the new iPhone 4? Obviously, I'd sell my 3GS to help fund purchasing the new SIM-free iPhone 4.
This way, I wouldn't tie myself up with a new contract.
I must admit, I'm quite confused with all the options.

I heard about Simplicity, but I'm not sure I understand it properly, and if it would be a good option for me. I thought it was a Pay-and-Go option, but then, I see they also have a 30-day and 12-month options, which is like a contract?
I don't even want to start considering other carriers, been with O2 for over 10 years, and even if they're not the best, it keeps things (already overly complicated!) simpler to just stay with them, as they'll all be more-or-less competitive (hopefully).
Hopefully, someone can advise and clarify any of the above raised points for me.
Thanks!