A lot of assumptions here, but they're not always applicable.
It all depends on how the student acquired the device. If it was new from the carrier and subsidized, I agree that's a big 2 year commitment - $1,200 or so if the line is on a family plan, even more if not.
But if a parent upgrades to a 4S, gives their 3GS to their kid, and adds a new line for it to their contract... well, the picture changes a bit.
At AT&T, that new line is about ten bucks, plus a one-time activation fee, and a data plan (So assuming 3GB of data, maybe $50/month total with tax).
That's not beyond the resources of a student with a part time job.
And.. because the device is a hand-me-down, there's no subsidized phone, no 2 year contract, no ETF. The line is month-to-month, cancel anytime. It's more affordable than people think, if done right.