I recall hearing a call from Europe (Italy I believe) and Antarctica - also from outer space.
Have people called from all the others: South America, Asia, Africa, Australia?
(I’m writing a book on MATLAB, a computer language for scientists and engineers, and am using some problems from the Puzzler, and I want to mention a few facts about Tom and Ray and the program.)
Over the years we have had questions from nearly everywhere. Often it concerns cars that we never see here. So far I can recall Australia, New Zealand, Europe, including Russia and other East European countries, Mexico, the Caribbean, Africa, South East Asia and the Middle East. Often the English is taxing.
Some times the questions come from US expatriates who know of out r website.
I’m referring here to email questions to Cartalk, not phone calls for Live Show.
Might want to click on the Blogs on the tool bar and ask there. I think the boys or their handlers are actually present sometimes there. Anything you would get from here would just be hearsay and unreliable-not that Doc is not reliable, which he is, but just not official for a book.
I love MATLAB. I wish physicists used it more than Mathematica. 
I had the opportunity about 20 years ago to work for Mathworks…but turned the offer down because my kids were young and the drive would be too much.
Back to the original question…They’ve also had calls NOT on Earth. Once they had a call from the Space Shuttle.