They actually do telemarketing on OMS residency. My uncle told me he's been called twice in a day about signing up to be a specialist. He slammed the phone and sweared that he's on the no-call list.
to answer ur question.. some of them are paid (recieve stipend). not a lot. Most General Residencies get paid and i think last years of OMS.. but a lot dont get paid..
search for this thread in the DENTAL forum.. not predental. they had a specific thread on this.