Probably a restocking fee involved as well as paying the difference in the cost of the phones, but you can always ask. I have seen them waive some fees on some items if you are buying some accessories or an extended warranty, etc.
if you are within those 30 days, you are just fine and they will probably charge you a restocking fee, BUT if you're out of the Trial Period, you're screwed... unless of course you sell it to an ***** (who's willing to pay more for it), and purchase the Bold at SRP price.