About 2-3 times a year I need to send a fax and like to whip out the old Apple USB modem for that purpose. Lion does not support it officially, but there is a workaround to make it work. How about Mountain Lion? Anyone tried it?
The workaround requires booting into 32bit version of the OS, which according to what I read is no longer an option with ML. You'd basically copy the required drivers from Snow Leopard, boot into 32bit mode and surprisingly it works. But I believe ML dropped 32bit mode so that won't work any more.