I’d quite like an iPhone but don’t want to be tied to a two-year contract. When looking at the TCO of most plans, you’re looking at something starting at £900 even for the most basic plans (75 minutes, 250 SMS and 1GB data).
Consider that O2 offer the iPhone on Pay as you Go from £449 (£440 on Orange) and you start to wonder what the extra £550 gives you. When averaged out on a two-year plan that gives you nearly £23 a month to play with. O2 offer a 1 month rolling Simplicity deal specifically for the iPhone giving you 300 minutes, unlimited texts and unlimited data & WiFi for £20 a month with a 1 month commitment.
Even with interest taken into account, getting a PAYG iPhone on your credit card and partnering it with a SIM-only deal from the same network is the cheapest way to buy giving you the benefit of a generous allowance and tieing you in for the shortest time.
If you want to be truly independent, you can get a SIM-free (unlocked) iPhone for around £800. You can get them cheaper, but they are usually hacked versions where you cannot update the software or you will relock the device to the original network.
Vodafone do not offer the iPhone on PAYG at the time of writing.