Amazon selling mobiles on contract
As of today, you'll be able to get over 90 phones on deals starting from £13 with nothing to pay upfront. All of Amazon's plans are 24 months long and are through the O2 network, should you care about those details.
There's some decent offers too. You can get the HTC One for £0 upfront and £28 per month (with unlimited texts and 1GB of data) or the Nokia Lumia 735 for nothing upfront and £15 a month.
Of course, this gives Amazon the chance to flog their own Fire Phone too, which you can get with a new Amazon contract. With unlimited calls and texts and 1GB of data, you can land one for £0 upfront and £28 a month.
Don't bother looking for an iPhone though because it looks like Amazon doesn't want anything to do with Apple. Not yet at least. You can check out Amazon's deals and phones here.