According to this YouTube video Walmart got the jump on T-Mobile with the BlackBerry 8520. The BlackBerry 8520 was scheduled to be released on August 5 but some guy named Alex says he was able to buy the 8520 at Walmart a few days early on August 2.
Walmart sells the 8520 for $48.88 with a 2-year contract. Check out the unboxing video.