After reading the title I knew that's where you were going.
The answer is no. I have a friend that was wanting one and didn't know this either so don't feel bad. It won't receive any audio input from your vioce so it doesn't transmit the phone call at all. It will for me at least transmit the audio for alerts while using it for say an email or text message for example. Also works for navigation audio, games, videos like native ones and YouTube. Just about everything on every device other than phone calls.
But you can pair a Bluetooth headset and connect them at the same time and the call audio will go to it while everything else will go to the Gateway. But all audio to the gateway will stop for the duration of the call then resume once your call has ended.
It's a great little device and if you think you want one, trust me do. I use mine daily and LOVE it!
I use it for my BlackBerry, HTC Evo, BlackBerry PlayBook, iPad mini, feature phones, iPod, wife's iPhone, the list could go on for a while. Works great on all of them.