Thanks to my colleague, Mary Jo Koranda, for pointing me to a service called inumbr, which provides you with a free, auto-expiring anonymous phone number that forwards incoming calls to your home or mobile phone. Callers do not see your home or mobile numbers.
I tried it out this morning and it worked as advertised. You have to tell it what area code you want for your anonymous number (the closest is Chicago area), then tell it how long you want the number to last (hour, day, week), and finally enter your real phone number.
After you hit submit, you’ll get a new screen with your new anonymous number. It will be a phone number with an extension.
To test out the system, I registered my office phone for the anonymous number. Then I called the anonymous number with my cell phone. The service did indeed ring my office number but there was a message that said that I’d reached the number through the numbr service.
So, people to whom you’ve given your anonymous number would know that there was something different about it, but not necessary what — unless they were also familiar with inumbr. All in all, pretty slick. See the FAQ for more info.