O2 officially sells the HTC Desire, one of the most popular smartphones around, for at least £30 per month with the phone costing at least £149 but use a third party like Dialaphone and you can drop the price to much lower than the SRP.
Indeed, buying the HTC Desire from O2 carries a minimum TCO of £689, a price that gets you 100 minutes, unlimited texts, data and Wi-Fi.
Should you be interested in the phone alone, you can get the same package, without the data and Wi-Fi for a mere £315 from Dialaphone which is less than half O2's.
The important thing is to remember to downgrade your contract after nine months from £20 per month to £15 per month otherwise the total cost of ownership will be £360.
The phone will be locked to O2 but then you can either get it unlocked elsewhere or use your exising O2 SIM, one from Giffgaff or Tesco Mobile.
As a reminder, the HTC Desire comes with a 3.7-inch AMOLED screen capable of displaying 800x480 pixels, a 5-megapixel camera with flash, a 1GHz Qualcomm processor and Google's Android OS.