Giant, I'd start the process now. You have to give 30 days notice (roughly) although you can say that you want it to finish at the end of your agreed contract if you can give about 3 weeks notice. I followed this procedure and would advise the same:
* Call Orange and say you are coming to the end of the contract and ask how they will accept cancellation: over the phone or by letter?; but say you are going to look around for a couple of days first as you have 'seen' various deals and phones at other networks - personally I will never deal with a 3rd party like Carphone Warehouse again.
* Ask for your PAC code as you plan to keep your number if you leave. It is your legal right (I believe) so they cannot deny you this. It expires after 30 days and you dont have to use it if you stay with Orange. This should be given to you over the phone and then confirmed by a letter.
* Start looking around for the phone you want and see which networks offer this - with me, it was only 2 networks - and find a deal that gives you the tariff you want. I, and others on here, would advise away from chequeback/cashback deal as it inevitably leads to hassle and not getting the great deal you expected.
* Using the information you have on the deal and phone you want, phone Orange (use SAY NO TO 0870 website) and say that you are looking to cancel and "What can you offer me to stay?". They'll put you through and offer you something which probably isn't that great. Say you think you can get better elsewhere.
NOW YOU HAVE A CHOICE HERE - follow through and have your contract cancelled at it's expiry if you are sure you can get a better deal elsewhere OR you can play the waiting game for a couple of days - if you want to stay at Orange.
* You should start recieving calls from other networks but more importantly from Orange themselves trying to keep you. This is where you can haggle and get THE best deal (and phone) Orange can offer you. Compare this to other networks and then I'd say to "give me a call after 24 hours as I need to talk to ??? (say a network you are comparing them with) as they offered you a better deal".
* In the next 24 hours call the other relevant networks stating what you have been offered and see if any can better it.
* Orange will call back where you can tell them yes or no. If yes, make sure they waiver any cancellation fee and make sure you know when your new contract starts. If no, make sure your contract is cancelled at expiration and you know when your PAC code will also expire as you want to take your number with you.
That's what I did and I stayed with the network I was on already. I've cut out the middle man now though and pay £10 a month for unlimited texts, 750 mins, a top of the range phone and a contract for only 12 months!