you are charged 49.99 for 30 days the money you have in your account is for mms mail or downloaded ringtones,apps or wallpapers if that total goes under $5.00 then they charge $15.00 to add to your "balance" this will also cover your overage costs. it can all be found in Boost Mobile's FAQ
i have it and like it alot beats most any sprintel account out there for what you get unless you work for the company or are getting a good discount