But if your car is equipped with GM's OnStar service, you don't even have to find your cell phone. The system can get help for you. It can also check your e-mail hands-free, make hotel reservations, and unlock your car if you've locked your keys inside, among other things.

Does OnStar work without a subscription?

It created a program called Crisis Assist, which allows all drivers of OnStar-equipped vehicles in a particular geographic area — even those without active OnStar subscriptions — to reach out to OnStar advisors for assistance with a wide variety of issues...

What cell service does OnStar use?

OnStar currently relies on Verizon's CDMA digital network to provide a car phone and slow speed data network to share vehicle diagnostics and enable certain remote functions. Current vehicle owners can continue to use OnStar services delivered over Verizon's wireless network.