this is my personal opinion. if you do call the office, you speak to the PC. don't underestimate the PC. in the majority of the programs, the PC plays a major role in screening the applicants. only the applicants that are chosen by the PC go onto to have their applications reviewed by the PD. again, this is for an unknown percentage of programs (other programs screen applications differently). see this other current thread to get a look at the role specifics of a PC in cardiology fellowship --
http://forums.studentdoctor.net/showthread.php?t=941759
anyway, i digress. i do not think you should call to facilitate an interview. it's really to see what's going on with the application status, whether invites have gone out already. maybe you missed the deadline when you submitted your application, etc. i do not think you should call the PD or even email the PD. that shows desperation. if anything, you should have your current residency PD to advocate for you, or a GI attending that has written a LOR on your behalf. they are really the best to validate your candidacy, rather than yourself.