If you must have an iPhone, keep in mind that they are not available though prepaid carriers.  Neither are most of the very latest and greatest Android models, but there are still decent and perfectly serviceable devices available through the prepaids.  There are also some pretty terrible devices like the Samsung Intercept, so do some research on the phones you are considering.  You generally have to pay significantly more upfront for your device.  The Triumph, for example costs $280 direct from Virgin Mobile, the carrier I use, but you can usually save by buying through Amazon; the Triumph costs $230, for example.

I switched from a traditional carrier (AT&T coincidentally), to a prepaid mobile carrier about two years ago.  I went with after considering a number of factors including cost, equipment and coverage area, but other prepaid carriers may work better for you depending on where you live/work.  One difference between AT&T and prepaid carriers is that some of the pre-paids don't have their own networks.  Boost and Virgin both use the Sprint network.  That is fine if you are in some area, not so good in others, so you definitely want to check a coverage map before making any decision.  You would not be a happy camper if there is limited or no service in your area and you only realized that after your purchase. 

The main advantage I've seen is cost savings.  The main disadvantages are somewhat limited coverage and difficulty reaching an actual human if you need customer service.  In fact, if you check the reviews of the prepaid providers, poor customer service is a common complaint.  That would be my greatest concern as a business user, where timely problem resolution is an important consideration.