Happens all the time, it’s called internship or apprenticeship: In this economy, it’s not just for kids anymore. Look through the resumes at any Craigslist location and you’ll see people offering a “free trial” of their services. It’s not the first tactic I’d recommend, but I do know of some that’ve got a good job that way.
From my experience, the “free trial” is a gimmick and nothing more. I never met a single person who got a job that way, nor heard of anyone doing so, and I have talked to alot of people.