Oh dear. Sounds like you've gotten yourself into a right pickle! I genuinely feel sorry for you. You made an unfortunate mistake, probably on impulse. It was one of those situations where it really was too good to be true. There is no point telling you that it was silly, you shouldn't have taken out the contracts etc etc because that isn't going to help you now! I can definitely understand how scared you must feel. £4300 is a lot of money right now. Unfortunately, I don't know much about the law but I do know that the phone companies will not simply write it off - you will have to pay for these phones one way or another. I have a few suggestions...
1. Could any of your friends/family take one of the iPhones off you? Say if they were looking to get an iPhone contract anyways. Either buy it from you or have the contract transferred to them. Maybe offer to pay £10 a month or something so that's an incentive for them to take the contract - they save a bit of money they were going to spend anyway and get their friend out of his pickle. If they wanted to buy it off you but couldn't afford to pay for it in one go, they could pay you back monthly and this money could go towards paying the phone bill.
2. Try and get some legal help. I know you are scared but from what other posters have written, you have not actually committed fraud - just simply taken out five phone contracts. I wouldn't go to the police, but maybe speak to a solicitor who deals with this area and see what your options are. You can usually get a free half an hour consultation with a solicitor. Following this, you are eligible for legal aid if you are a student or on low income (I assume you are on JSA?). You'd be surprised, sometimes those working in the law profession can find loop holes that open a door for you.
3. Let go of your pride (I know =() and tell your parents. If they are able to pay it off for you then this replaces all of the above hassle and all you have to part with is a little dignity. Yes, they will be disappointed/angered and you will feel ashamed, but this is much better than bailiffs turning up at your door - right? You can always pay them back over time, and if you can't afford to start paying them back straight away you can repay them in other ways. Start doing things around the house - cleaning, washing up, cooking dinner, bringing them breakfast, tea, coffee etc. No doubt your parents will be annoyed but at the end of the day they are your parents, they are human and they know you and love you. They know that people make mistakes and have probably witnessed you make them throughout your life and now it is time to face the biggest mistake.
3 is my preferred option.
I know you want to do this by yourself and keep your pride, but honestly, I don't think you can. Tell your parents.
Good luck.