I had the same type of call, calling the number back yields the same recording stating it was for a rebate redemption. The funny thing is that I don't have any type of rewards outstanding.
Same experience as others. Pressing 1 gets you a sleazy sounding person who gives you a line of crap about gift cards and tries to get personal info. I have gotten calls like this before and I know for a fact Wal Mart does not run any such promotions. Clearly a scam.