Last month BGR confirmed that Sprint would be launching an instant rebate promotion that eliminated mail-in rebates and instead brought users instant savings. At that time, Sprint told us that the promotion would continue for an unspecified period of time. According to a purported internal document obtained by technology enthusiast blog Spantechular, the carrier will end its instant rebate promotion on May 7th. With Sprint rumored to be launching the BlackBerry PlayBook tablet one day later on May 8th, the timing certainly adds up. When approached for comment, a Sprint spokesperson told BGR that the carrier has not announced an end date for the instant rebate promotion.