Existing card “A” with 15,000 charged on it. Of the 15,000, 11,000 is charged in regular purchases being billed at 9% APR and 4,000 in a cash advance being billed at 15% APR.
A competing credit card “B” this user has, but has not used in some time, on which there is a zero balance, offers the option to transfer the card “A” 15,000 balance over to card "B" for a 3% transfer fee and 0% APR until October 2012.
The 450 transfer fee (3% x 15,000) would be added to the amount owed so it will now be $15,450 balance on card “B” . If it looks like the credit card user will not be able to pay off card “A” debt immediately this looks like a better deal than keeping it on card “A”.
As stated, yes, as long as the cardholder will be able to pay off the balance before October 2012. If not, then the interest rate charged on “B” after that period matters.
Sometimes they slip in a clause that if the full amount is not paid off by the end of the no-interest period (Oct 2012 in your example), then they charge interest back to the original date, at their prevailing rate. In that case, depending on what their interest rate is, it might be better to keep it on the current card.
For what it’s worth, the first time I took advantage of a balance transfer / zero interest offer, there was no such clause (and, nicely, the transfer fee was capped at 50 dollars). But you do have to carefully read the terms of any such zero-interest offer (e.g. “same as cash” deals from stores which can be insanely punitive).