Your registration will not expire. Telephone numbers placed on the National Do Not Call Registry will remain on it permanently due to the Do-Not-Call Improvement Act of 2007, which became law in February 2008. Read more about it at http://www.ftc.gov/opa/2008/04/dncfyi.shtm.
The National Do Not Call Registry gives you a choice about whether to receive telemarketing calls at home. Most telemarketers should not call your number once it has been on the registry for 31 days. If they do, you can file a complaint at the DoNotCall.gov. You can register your home or mobile phone for free.