HTC ONE £22p/m with 600mins - Unlimited txts - 750MB data - £50.00 handset (£50 OFF with code!) £578 total cost @Mobiles.co.uk
24months @ £22p/m on O2
Free next day delivery
£578 total cost.
All you need to do is refine your search on the left-hand side of the page by selecting O2, then choosing 500-1000mins, and 500-1GB data.
Then scroll to the bottom of the page and you will see the deal.
Add to basket and enter code FBFREEHTC to get £50 off the handset price (Usually £100).
Plus a possible £27 cashback available through Quidco.
NOTE - They will add 'VIP Gadget Helpline' to your contract which is free for the first month and £3.99p/m there after. But you can cancel it at any time once you receive the phone and won't be charged a penny. So make sure you do this.