We are in the middle of an AS9100 program, and I dont' remember anything about a recommended frequency - although most of the standards are open-ended enough so that you can make your own determinations as to the frequency, again, depending upon the kind of work that you're doing.
Our optical comparators and several other larger pieces of equipment are done annually. Most of our other stuff is done on an as-needed basis; that is, when a job needs a certain micrometer, gauge, etc., it's calibrated before it hits the floor and checked against the QC standard. We may not need that piece for another 6 months or two years, so there's no point calibrating it when we don't need it.