Last time I bought a new phone, I noticed I could either pay at once or split payments over two years at 0% interest. For clarity, the 0% interest option meant the sticker price of the phone would be divided by 24. No interest, no hidden payments.
The second option was better mathematically. Taking a 0% interest plan meant I could keep my lump sum and do something else with it. If I stuck it in the safest investment at ~ 1% per annum, I would still end up a few pounds better after two years compared to if I paid it all upfront.
But there was no way I was taking that option. In fact, I would rather buy a cheaper phone with cash than a nicer phone on a 0% payment plan. Why? Because I know myself. I knew the angst of watching the money drip out over 24 months would outweigh the few pounds I would gain or the utility of having a nicer phone.