I was out of contract. I got it by just walking into one of the shops. It's an offer available to any customer with XL landline phone package (who hasn't already taken the £8 mobile discount already). If you are on M or L phone you get £5 off so can get it for £25.99
Had planned to keep my Desire and downgrade to a SIM only tariff until after the Android 4.0 launch event but got impatient