You will need:

An inferior touchscreen phone,

Some tinfoil and polystyrene,

A soldering iron,

An empty iPhone box and

Imitation O2 contract paperwork.

Jimmy the phone until it looks like an iPhone.  Download a photo of the iPhone home screen and use this as the background wallpaper.  March into the O2 store and make it very clear from your manner that you are rich and irritated.  Complain that this is the seventh time your iPhone has needed repair and you are very unhappy with the quality!  Tell them that you considered litigation for breach of contract since they have failed to provide you with the suitable working equipment you paid for.  However, you are prepared to resolve the situation calmly if they will simply sell you a second contract on the newer iPhone 3GS at a cheaper rate.