Can You Unlock Car Doors Remotely using a Mobile Phone?

I was watching a gadget show on TV this week (the channel was either NDTV or IBN) where this  gentleman demonstrated how to unlock the door of your car using just a mobile phone and a spare set of car keys that are lying at your home.

Here’s what they did to unlock the car with a cell phone and the remote key:

1. Man gets out of the car, closes the door but then realizes that he left the keys inside.

2. He calls his wife at home using a cell phone and asks her to hold that duplicate set of car keys near her cell phone.

3. He then held his own cell phone near the car door while her wife pressed the unlock button at home. The car door gets unlocked immediately.

I may have treated this as a hoax had I read this trick on some web forum but since this procedure was shown on national TV by a reputed channel (with a real video), it may not be completely baseless.