can i send a fax?

A further question is how do you want to send a fax, and at what monthly volume?

1. Internet fee-based, Fax service? The first 3 have an IOS app too.
   1. eFax (app store)
   2. MyFax (app store)
   3. PopFax (app store)
   4. InterFax
2. Connected USB Fax modem? Starting with Lion, the Apple USB Modem is unsupported.
   1. Zoom 3095 USB Fax Modem here has been reported to work. No audio. Plug/Play. No drivers.
   2. US Robotics USR5637 56K USB Faxmodem. Here. Review stated works with ML as of Aug 2012.
3. Connected (and supported) multifunction device?

Here is Apple's Mountain Lion sheet on Fax.

A look at the Mountain Lion Fax interface.

If items 2 or 3, you will need to search for devices that are stated to be compatible with OS X Mountain Lion. If multifunction device, that would also be specific stated support for the Fax functionality.