What does this Electronic Gadget do exactly...?

Wilson Electronics 815226 Sleek Cell Phone Signal Cradle Booster for All Cell Phones with Mini Magnet Mount Antenna - For Single User

Reduce dropped calls, increase 3G data rates in weak signal areas and originate calls from dreaded "dead spots" with the Sleek Cell Phone Signal Cradle Booster from Wilson Electronics. The Sleek and its external vehicular antenna increase any phone's output power to the cell site while improving its ability to hear signals it normally cannot, keeping you more reliably connected. It extends the calling range and signal strength of any phone


What is this... The purpose of it?

Your last sentence tells it all. It extends the calling range and signal strength of any phone... but for use in a vehicle, you will also have to have bluetooth to use it legally in most states.