Don't plan on that 10% discount unless you are buying the phone outright. Our discount doesn't work on the subsidized price.
I use to run the connection center a few years ago. If you are lucky your store has a guy like me who knows (well knew...) the plans inside and out. Go talk to them, they can get you the best deal.
Working for Wal-Mart you get a discount on your monthly bill from most of the carriers. Don't forget to find out how to get that. For some silly reason we cant apply that in store, unless something changed.