What is full-time vocational ministry, really?

[mounty] This is a question that I’ve distilled from a much larger and more complicated set of issues in my life right now, but I wondered what you guys have to say to this facet. What does it mean to be in full-time vocational ministry? I know that’s really vague, so let me elaborate. I don’t think anyone would argue that a man who spends his working life during the week fulfilling the responsibilities of a modern pastor (studying, visiting, witnessing, leading his flock, etc.) would be considered to be in full-time vocational service. But what about the church business manager who shuffles paperwork for the church during the week and draws a salary from the church doing so? Moving away from church, can, say, a secretary working the front desk at the home office of a missions board be considered in full-time vocational ministry? And what about those whose qualifications and certifications are secular in nature but who use those in a full-time capacity, like a science teacher at a Christian school? What about a Christian science teacher in the public school? And what about the guy who works as a plumber during the summer at a Christian camp and a general contractor the other eight months out of the year?

I’m not putting up these examples and saying “please comment on each.” I’m using them to show that there’s a lot of types of jobs at a lot of types of employers which, by their very nature, are designed to advance the Kingdom purpose. But where is the line between “working for a Christian organization” and “in the ministry” to be drawn?