Most carriers require that you sign up for a data plan when you buy a smartphone. Again, Sprint charges $10 a month for unlimited data--that's the same fee that covers the texting.

AT&T and Verizon offer cheaper voice plans than Sprint, but they make their money back on the data side. AT&T offers a base plan of $15 per month for 200MB of data; go over, and it'll charge you another $15 for every additional 200MB. Its 2GB plan is $25 a month; slightly better than Verizon's 2GB a month for $30. However, if you regularly use more data, but aren't quite ready to shell out for the Unlimited options, Verizon offers additional tiers at 5GB ($50 per month) and 10GB ($80 per month).

Each carrier also offers hotspot capabilities, letting you share your iPhone's cellular data connection with other devices, like an iPad or MacBook. requires you already subscribe to its top-tier 2GB data plan; on top of that, you'll pay another $20 per month--though you'll also get an additional 2GB of data. Verizon , which can be added on to any of its data plans, and Sprint offers a $30 option.

Of course, coverage is a comparison we can't really make for you. The advantage here depends on where you live and how you use your iPhone--and if you, for example, live in the suburbs but work in the city, it can get even more complicated.