Where to buy Desire Z?

[Guest orangephone]

I have been on Orange contract for nearly 2 years and due for an upgrade. They have some low end phones available but also ones like HTC Desire etc.

I've only been on their £15 a month contract but much prefer giffgaff which I haven't switched to yet (I need calls to the same network as myself).

What should I do? Upgrade and sell the phone, then buy a Desire Z, or look elsewhere?

I read on this forum there is one available on Orange here http://www.e2save.com/mobile-phone/contrac...C-Desire-Z.html but it costs £25 a month and I'm not sure I'll be able to afford that. Unfortunately the Deaire Z isn't available on the list of upgrade phones on their website.

Is there somewhere I can get the phone for a good price (with cashback using TopCashBack) and then stick a £10 goody bag giggfagg sim in?