CraigsNumber will provide you with a free, anonymous phone number that expires after the amount of time that you choose. The idea is that when you're posting to CraigsList or other online communities, you don't want your real phone number to be out there forever for crazies to call you. So you can get a temporary number at CraigsNumber, which will forward incoming calls to your real phone number.
You can have your number, in your choice of 23 U.S. cities, expire an hour, day, week or month from when you set it up. Options let you block certain calls, activate voicemail, and receive your incoming call history via e-mail.
You can also get started at the CraigsNumber web site or by calling (415) 234-5678.