A little over two years ago I ditched my trusty Nokia phone and got an iPhone. No regrets there, but iPhone did come with a hefty 24 month contract with Vodafone costing in theory £30 a month (in practice closer to £40 due to some extra charges that I never understood).
With this contract having expired, I've since switched to a simple pay-as-you-go SIM. The cost, so far, has been less than 50p a week.
That's more than a 95% saving.
I didn't think it'd be quite that cheap, but then I don't make very many mobile phone calls (and when I do they're typically short), and whilst I'm using the data connection on the phone quite a lot, that's mostly when connected to a Wi-Fi network.
Also, most of my text messages now get routed through Apple's iMessage servers rather than via SMS.
It all goes to show just how much you end up 'paying' for the phone when getting it cheap/free on a contract. The psychological appeal of not having to pay a large amount up-front has a very real long-term cost.
As a side-effect of moving to PAYG, I'm now holding off from 'upgrading' my phone until I really need to - and the £500 cost of doing so is being more fairly weighed against the other things I could spend that money on.