You signed up for a contract mobile phone and accepted that it was costing you a bit for the service and a bit for the phone. Mobile phones are very expensive and the cost gets subsidised by the carriers so naturally we have to pay them quite a bit while we’re under contract.

But you don’t stay under contract. After two years, say, the contract is up. Yet people keep paying their regular monthly bill anyway.

I went a bit pale this week when friend-of-the-blog Steve Fitzpatrick pointed it out. Fortunately, I think I have always gone from one subsidised phone to another. But not this time.

This time I am just out of contract but I haven’t bought the new iPhone. So on Steve’s advice, I went back to my carrier and changed my deal. Now that my contract is up, I own my iPhone 5 so for now I’m keeping that and only paying Three for the service.

The difference is huge. I used to pay £42/month and as of this week, that’s down to £18. It’s a slightly better deal in terms of texts and phone minutes but who cares? It’s the all-you-can-eat data that I wanted enough to pay £42 for but I now have for £24 less. Per month. That’s a quarter of a hundred pounds less.

So thank you Steve. And if you’re in this position, go change to a new contract. Specifically a SIM-only contract.

Curiously, two reasons led to the conversation with Steve that got me this saving. One is that there are two iPhones out and they’re big. I need to see them in my hands before I can really decide whether they’re too big for me or not. There are reasons to like the new iPhone beside size but the size could put me off. Consequently I didn’t just pre-order or plan to buy on release day today.

But the second is that I couldn’t really make the numbers work. The price of the phone under a two-year contract is fine but no matter how I sliced it or how I considered switching to other providors, I didn’t like the numbers. All you can eat data is important to me and every deal was coming in at £45 or above.

Now I’ve gone SIM-only and own my iPhone 5, I’m suddenly looking at £18 a month I’m actually paying or anything above £45. That’s a big difference. That’s a big enough difference that I might skip this iPhone.

Incidentally, if I don’t skip it, if I go buy one, I am now committed to my SIM-only deal for £18. I couldn’t get a subsidised iPhone 6 from Three without paying some terminations fees. But I could buy one from Apple and pay over Apple Finance to get a monthly fee. That’d mean paying Apple a bit every month for the phone and Three a bit every month for the service.

It works out at pretty much exactly what I’d have been paying if I had gone straight for having Three subsidise me.

So I’m no worse off with my potential decisions but I am much better off with what I’m actually paying. And I go so pale at the thought I might very well have continued to pay my old monthly cost forever. You know people must do this. You know mobile phone companies would let them.

If that’s you, then, go sort it out and thank Steve.