I have received 3 checks from them, each for about $200. Perfect service, no hassles, no delays.

The only way in which it can be scam-like is that sometimes you may do better in the end by signing up for a plan that doesn't offer cash-back, but has rates more than 10% lower than the cash-back you're on. Cash back sometimes is a good deal, and sometimes isn't.

Definitely what Sprint counts on though is people forgetting to cash in their balance. That's why they don't just automatically send it to you. Once you ask for it, however, I'm pretty sure they send it promptly.