The Order of Special Full-Time Servants appears to be a religious order of Jehovah's Witnesses. What is a religious order in the context of Witness theology? Is it theologically meaningful at all? To what purpose do people join this order? When do they leave? (Do they leave?) How does the whole thing work?
I spent a great deal of time searching for an answer to this that doesn't make it sound like a scam to avoid taxes and enjoy the benefits of being treated as a religious institution, but I couldn't. As is usually the case, it's a lot easier to find information from those that stand against the Jehovah's Witnesses than it is to find positive information about them.
According to outsiders it's little more than a tax dodge as stated in these first few links.
However... The most complimentary description was found in a legal document from the Oregon Judicial Department Apellate Court This seems a little less inflammatory. It describes them as people that have simply dedicated themselves to ministry, and therefore would function in a way that assists the Church. As such, their right to tax-exempt status is less clear.
However, this question isn't (as far as I know) about their tax-free status, but about what they are, and what their function is. Unfortunately, the following is the best, least inflammatory description I could find. Since they don't have information about themselves online anywhere, this is what I'm settling for providing. It's not first-hand from them, but presumably it's based on first-hand interviews with lawyers that are familiar with the defendants. It's better than nothing.
Full time ministers of Jehovah's Witnesses are those that spend a minimum of 70 hours in some form of Christian service. By far the vast majority of these ministers also work and pay taxes.
A proportionally small number work in the Jehovah's Witness Branch offices and are offered logding and a small allowance and others are missionaries and travelling ministers that also get a small allowance from the organization.
Whether these individual pay taxes dépends on the law of each country but many do not because their income is so very low they are non-taxable.