Well I read the fine print and it says as long as the minimum payments are made on time the 3.9% remains until paid in full.  Doesn't hurt to call and get the full story though.  I considered doing it to pay off my car for the slightly better rate.  My car is financed at 6% and I owe about 9k left, but seeing as how I pay extra every month, and it will be paid off early, and I'm lazy, I decided not to, lol.