He uses a FEIN that he's had for 7 years now. I don't recall filling out any form regarding how many employees or having to show our tax returns or anything.

Of course, there is no phone # at all on this letter they sent.

For whoever asked, the free electronic claims service I use really is free. I've been using it for 1-2 years now. They only charge .25/claim if they have to drop it to paper and the only insurance that they can't bill electronically yet that we bill frequently is Medicare and then the occasional Podunk Nowhere Insurance Company. I know that Medicare has some kind of free electronic claims software but I don't think it's compatible with my version of Medisoft and I don't want to have to input everything twice.