some people say yes, some say no. the general consensus is that they do not call. they will, however, most likely question you about it in the interview. if you lied, they will know. and lies are bad.
they do spot checks. i've posted this before, but i'll tell again. when i was working in a community clinic answering phones, vcu called to verify dates of employment for an employee who worked there before me.
don't know how common this is, but if one school did it, i'm sure others do too. there's no way they always call every contact, but like i said, SPOT CHECKS.
I don't know about other schools but I was looking at the University of Rochester's website and they say, explicitly, that they check on the activities you listed. In fact, it says something to the effect of your acceptance is contingent upon verification of your activities.
You'd better believe they do. My medical school had a Verification Section in the Registrar's office that did nothing but check all of the things applicants put on their AMCAS application.
When I was a second year they called me in to discuss an article for JAMA that I sort of claimed to have authored.
"JAMA?" I said, "Oh no, I meant Big Bad Mama-Jama...you know...the girly-mag."
Suspicious looks from the registrar.
"Surely you've heard of it? No? How about its sister publication, Bootilicious Tatas?"
It wasn't really an article. More like an appreciative letter to the editor but it was published. "May 1992. I think you can get back issues on-line."
Not bloody likely but in medical school, as in life, you have to think quickly. I bet they're still trying to sort it out. I graduated a year ago so I think I'm in the clear.