Donna Murphy got her first Broadway job (THEY'RE PLAYING OUR SONG) through an open call while still an undergrad at NYU. Most of the OBC of MERRILY WE ROLL ALONG (Jason Alexander, Tonya Pinkins, et al) were college students with no Equity credits when they were cast.
Didn't the 42ND STREET revival have a tap dance contest open to the public to cast a couple members of the ensemble?
There are LOTS of performers who got their first Broadway gig through non-Equity open calls.
"What a story........ everything but the bloodhounds snappin' at her rear end." -- Birdie
[http://margochanning.broadwayworld.com/]
"The Devil Be Hittin' Me" -- Whitney