I didn't realize this until recently, but the problem with the toll free numbers and why they are inactive after a short time is that they are posted here on the boards. The toll free number is designated for travel agents only, and usually a TA will share the number with the board. Disney gets bombarded with calls to that number and they close it.
Some ideas to saving $$ calling 407 WDW DINE:
If you have a cell phone, most plans have free nights and weekends and Disney Dining is open 7 days a week. You could call them for free on the weekend.
If your long distance is expensive then perhaps you'd have better luck with a calling card.
I know it's a pain and it seems as if Disney should have a 800 number for us, but they don't as of right now and they seem to be working hard to keep the 800 number out of our hands.