What is the deal with mail-in rebates?

I don't even know what the ostensible justification is for a multinational corporation borrowing my cash for eight to twelve weeks. Are they earning interest on it? Are they building an impenetrable Illuminati bunker in the mountains of Colorado? Are they arming guerrillas to thwart an oppressive regime that subsidizes a competing cell carrier? I'm pretty sure I need money more than you do, Cellular Giant, so what gives?

As far as I can figure, the people who formulate these rebate schemes have two primary objectives: get you to buy a phone, and find a way not to pay you. Of course I could be wrong, but experience tells me this is the case. The idea of a rebate is to entice you. It used to work on me. My purchase decisions were influenced by mail-in rebate incentives. Then, I'd walk out of the store and forget to mail anything in. Or, I'd forget until it was too late. My consumer life was the perfect example of a rebate scheme going as planned.

As I got older, I became a bit more responsible. I started mailing in the rebate forms the second I got home from the store. Guess what. I received more letters notifying me that I wasn't eligible for a rebate, or requesting additional information, than I did checks. I've classified the mail-in rebate as a con in quite a few reviews on this site, and with good reason. I know each company is different. But how many times can a consumer get the shaft before becoming weary of a sales technique? Of the dozens of rebates I've sent in during my life, only once did I get paid. It was for a hand-held label printer, and the rebate value was under $2.00.

The last straw for me was regarding a $50 rebate on a phone I ordered from T-Mobile in 2006. The same day the phone came, I sent in a copy of the receipt and the required form. I printed the form out and typed in the answers with a typewriter. I didn't want to give them any excuses. Three weeks later, I got a letter saying the form was illegible. I called the provided number and they assured me that the four week time limit didn't apply, as I had sent in the original on time. I resent the form and receipt, and I waited. And I waited. And I waited. About three months after getting the phone, I finally got a letter saying I wasn't eligible for the rebate because my letter arrived outside of the accepted time frame. No number was given this time; no offers to address further concern. This was... Goodbye. Of course, the rebate team was a separate entity from T-Mobile proper, so I had nowhere to turn. 
 
I'm not saying we should boycott all products marketed with mail-in rebates. And I've never tried to recoup money from most of the companies whose products we review here. I'm just saying that the people who come up with the marketing gimmicks you see when phone shopping are not paid to make sure you are a happy customer. They are marketing experts. The suits who contrive rebate schemes are hired to make money; not to give it away. They also aren't the ones who have to answer the phone when you're trying to find your $150.00. Buyer beware.