Depends on the term mass-market success, of course, but generally speaking, in today's market, no (this being my strictly personal opinion everybody is welcome to (dis)agree with). However, a slow shift in business models (which are long overdue in some indrustry branches) just may make it a mass-market success in a rhethorical tomorrow - like it happened before with linux on the server market. This change, however, won't happen overnight. Remember, there have been loads of Linux phones/MIDs out on the market - it's just that they were never marketed as such. It also needs support of some key players in the field. Enter Nokia with Maemo (or, I must mention, Google with Android), which gives the oft-spoken about potential to really push stuff mainstream. Reminds me a bit of IBM and their Linux transition/adoption.