From the (Ann Arbor) Community High email newsletter I learned the following:
31 days from today, cell phone numbers are being released to telemarketing companies and you will start to receive sale calls. YOU WILL BE CHARGED FOR THESE CALLS… To prevent this, call the following number from your cell phone: 888/382-1222. It is the National DO NOT CALL list. It will only take a minute of your time. It blocks your number for five (5) years.
You can also visit the national do not call registry online and register your cell phone (or regular phone) there too.