Surely it should just be a matter of walking into the carrier shop, getting a pay-as-you-go SIM card, and paying for calls as you go along and a few bucks extra each month for data? Quite economical unless you make loads of calls.
And how on earth do the carriers get away with mandating an expensive data plan? O2 here in the UK does require a data plan on standard iPhone contracts, but the cheapest data plan is £3/month.
What I love about my iPhone is ubiquitous...