If you've ever lost your mobile phone, but didn't have another line to call it to make location-revealing sounds, Google Voice's call feature will help you find your phone by calling it for free.
While making a call on Google Voice, you can select which phone number you'd like to make the call on—in this case, the phone you lost. After entering a phone number you want to reach, Google will first call your mobile phone, wait for you to pick up, and then connect the other end.
If you're one to lose your phone frequently, you should call a free-number like 1-800-GOOG-411 to avoid pissing off all your contacts—or your parents, in order to punish yourself for losing your phone again. [Google Voice via Lifehacker]