No sorry I have no idea either.
We only have our mortgage too and when we upgraded my car which was just after our wedding before we had Brandon we just extended onto the mortgage.
We have a credit card but we dont use it unless we buy something over the net or have to book a motel or something with it over the phone. We never use it other than that.
Sorry couldnt be of more help, I have heard of this I think but not sure who or how it works etc.