Sprint Playing Games?

Sprint has this new deal for existing customers where if you have had you cell phone for more than 18 months and it has been at a rate of $34.99 or higher during that time, then they will offer a $150 mail-in rebate on a new phone.  The catch?  You have to pay full price for the phone first, and then wait 6-8 weeks for a check to come in the mail. The question? Why?  Why not just offer instant rebates to customers and keep us happy?  The answer, because (i) they don't get to generate the interest on your payment during the time that you are waiting for your rebate; (ii) some customers won't bother with applying for the rebate; & (iii) that would be too sensible, and good customer service, so why bother doing that?