Actually, Phi Mu Alpha Sinfonia
is a social fraternity, as is Sigma Alpha Iota.
Phi Mu Alpha was founded in 1898 as a social fraternity, albeit a social fraternity geared toward men studying or interested in music. During the mid-twentieth century, the Fraternity began to act more like a professional fraternity and to consider itself such, although it never required that members be music majors or minors. (There are chapters now with no music majors or minors in them.) This shift was in full swing by the 60’s and 70’s, although the Fraternity always kept a foot in the “social” side. In many ways, it acted more like a “social” then a “professional.”
Then came Title IX, which required single-sex professional fraternities to go co-ed. Two of the music sororities, Mu Phi Epsilon and Delta Omicron, did just that. Sigma Alpha Iota sought and received from the federal Department of Education a determination that it is a “social” sorority, and thus stayed all-female. Phi Mu Alpha Sinfonia decided in the early 80’s to place itself firmly on the “social” side as well; it also received a ruling from the DoE that it is a social fraternity. Most “professional” references were removed from all Fraternity documents and publications at that time, although there is still some “clean up” going on.
Phi Mu Alpha has not joined the North-American Interfraternity Conference, although I understand that consideration has been given to doing that. Nor has it ever amended the Constitutional prohibition on membership in any other music fraternity, as opposed to any other general fraternity. Individual chapters can decide on their own whether to join their campus’s interfraternity council (or similar group) and be bound by such things as rush rules. My understanding is that many have done so and more are exploring the idea. Other chapters operate much like they always have, somewhat to themselves. On some campuses, then, Phi Mu Alpha still looks somewhat like other professional fraternities. On other campuses, Phi Mu Alpha is virtually indistinguishable from the other social fraternities - except for all the singing.
In any event, Phi Mu Alpha Sinfonia is a social fraternity.