Fincen called me back. ... He had no idea
Yeah this is the hard part
If you get someone knowledgeable on the phone
MSB is an umbrella term. A money transmitter (or check casher, or issuer of prepaid access) are all MSB. All Money transmitters are MSB but not all MSB are money transmitters. FinCen has no specific "Money Transmitter" registration. They register MSBs. They register check cashers as MSB, issuers of prepaid access (stored value) as MSBs, and Money Transmitters as MSB. There are seven activities which a company can declare when registering as a MSB. It is possible for a single entity to be registered as an MSB conducting more than one activity (i.e. WU is a money transmitter and also issues money orders).
From the source....
(ff) Money services business. A person wherever located doing business , whether or not on a regular basis or as an organized or licensed business concern, wholly or in substantial part within the United States, in one or more of the capacities listed in paragraphs (ff)(1) through (ff)(7) of this section. This includes but is not limited to maintenance of any agent, agency, branch, or office within the United States.
(1) Dealer in foreign exchange. ...
(2) Check casher ...
(3) Issuer or seller of traveler's checks or money orders. ...
(4) Provider of prepaid access ...
(5) Money transmitter ...
(6) U.S. Postal Service. ...
(7) Seller of prepaid access. ...
http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&SID=1308d21216c7d185f6892cfa3276c899&rgn=div5&view=text&node=31:3.1.6.1.2&idno=31#31:3.1.6.1.2.2.3.1