It was roughly six months ago, but I'll never forget this chilling statement from a neighbor with whom I was discussing my experiences in Fooldom: "No one pays attention to their money. If I mailed a bill that said 'services rendered' to everyone in this development I bet I'd get back at least 100 checks." Our housing development in suburban southwest Denver boasts more than 600 homes.

Chilling? Sure. Accurate? Yes, surprisingly so.

Recently I was reviewing some of our bills and was taken aback by the size of the monthly invoice from Qwest (NYSE:Q), our local phone carrier. It turns out we were getting charged by two long distance providers -- Sprint (NYSE:FON), my carrier of choice, and MCI (NASDAQ:MCIP), my former carrier.

Here's the rub: In early 2003 I switched to Sprint after having MCI for more than four years. Not only did I not like what had gone on with the firm's books, but also UAL Corp.'s (OTC BB: UALAQ) United decided it no longer wanted to offer Mileage Plus miles through MCI, switching to Sprint. So I followed suit and got a lower rate and the same miles deal. Brilliant, right? Not exactly.

The problem is that I never called MCI to cancel. I thought by signing docs that authorized Sprint to be my long distance provider that my MCI service would simply be stopped. But it never happened. Instead, I spent 18 months blindly paying the minimum charges to MCI with each phone bill. The total came to more than $145. Ouch.

The kind MCI operator who helped me confirmed that Qwest should have notified MCI to cancel the service, but she also pointed out that it's my responsibility to manage my account. She's right. I goofed. After making a $45,000 mistake in 1998 you'd think I would have learned my lesson. It seems even the Foolish can never be too careful.

The good news is that I'm receiving a credit for the whole $145 over the next two months, plugging a substantial hole in my leaky wallet. But it's the opportunity cost that really hurts. I could have put that money in an S&P 500 stock index fund, dollar-cost averaging my way to better returns.

Can I promise this will never happen again? No, of course not. But you can bet I'll be looking at each bill a lot more carefully from now on.

Don't tolerate a leaky wallet. Make sure your credit is in order, and that you're getting the best savings deal you can get. And then, when you're ready, join other Fools in learning to live below your means.

Fool contributor Tim Beyers is embarrassed to admit that he has a leaky wallet. He's working on plugging it. Tim owns no shares in any of the companies mentioned, and you can view his Fool profile here.