I ran across this blog article explaining how the Do Not Call List will expire for the very first people who signed up. When you sign up, it is good for 5 years. I checked mine and am good through June 2008.
You might want to go ahead and check your registration to make sure there is not a lapse. Telemarketers have to check the list every 30 days.
I also setup a Google Calendar event just before mine is about to expire so I can recheck and make sure I am on the list for another 5 years. FYI: I have both my house phone and my cell phone on the list. This is just to make sure I don’t get any un-expected calls if I can avoid it.