well they charge you for the item and will hold it at the store for 2 weeks. If you don't come pick it up, it gets returned to your card and returned to stock.
But make sure if you do a charge hold, you get the SA's name, the total amount, and write this down on a piece of paper along with the date and time you called as well as the store info.
If you just want to do a regular hold, they will only hold it for 48 hours, no cc required.
