I like the idea a lot. This is one of the cases where most people try to fix something by calling even though they would be much better off sending in a form letter. Check your contract. It probably says something along the lines of "service will be terminated within 5 business days after written notification" but they sure don't guarantee anything good will come from calling customer service on the phone.

I would be a little worried about basing a business on this because someone else could start a site with a free collection of the letters to download. Until then this would be well worth the money.