You are not supposed to be able to do this, due to port blocking and regulatory issues. In reality I have received calls on my phone while under Gogo, and the first time it was from a number that I knew might need me urgently. Luckily my phone was on silent ringer, and I picked the call up and super quietly told the person I would have to call them back in a couple of hours. Grand total of time on the phone was 20 seconds.

At least twice more I have had calls come up while on Gogo, but I would not answer them (I always turn my phone to silent when I am online while flying).

YMMV