Oh, another one of these threads?
I don't know about the US, but in the UK there are some really good deals without a two year commitment. One month rolling contracts are very good, for example: £25 a month for 2000 minutes, 5000 texts and unlimited internet with tethering is
an amazing deal.
Giffgaff has even better deals than that (and only do pay as you go, no contracts) but I'm moving away from them because their service has been declining a lot as of late and they don't allow tethering.
Generally speaking, if you upgrade your phone every year and sell your old model, using one of those plans and buying the phone outright is a better deal if you do the sums on the equivalent contract options.
However, if you plan to keep the phone for more than a year, the contract may be better because the phone will lose more resale value by then and your network may give you a better deal for upgrading with them than you would if you just bought another phone outright and kept using pay as you go.
So there's really benefits to both sides. Personally I've tried to stay away from committing to a 24 month contract but I might sign one to get a cheap iPhone 5 anyway, especially since I'm already looking to get away from giffgaff. Plus I'm trying to get a job at Three at the moment and if I get it I'll be selling everyone contracts whenever possible, and it'd be kinda hypocritical not to use one myself wouldn't it?

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In the UK, the monthly costs with of without a phone are considerably different, subsidised phone plan could cost £40-50 a month, equivalent sim only plan is only £10-15 a month.
Buy the phone outright and choose the right plan and it can cost half to 2/3rds of the cost of network subsidised + contract.
Not to mention the advantage of moving supplier when a newer better plan is launched.
Not always. On Three you can get
an iPhone 5 for £79 and for £34 a month you get 500 minutes, 5000 texts, and unlimited data. That same deal without a contract saves you less than £10 less a month but then you have to pay over £500 for the phone.