At a Q&A session this afternoon, Mozilla CEO Gary Kovacs mentioned that he expects Firefox OS phones to hit the US "somewhere in the 2014 timeframe." That would be after the first round of launches that are being spearheaded this summer, mostly by European carriers with global presence in emerging markets and areas where smartphones running iOS and Android haven't already taken hold. (The ZTE Open being shown here, for instance, most certainly won't be sold by an American carrier.)
But which carriers? Kovacs simply says that Mozilla has partners "lined up," but considering that Sprint is listed as a "special guest" at today's Firefox OS event, it's a safe bet that they'll be in the first volley.