step one: enable wifi tethering on your android:
go to settings>wireless & networks and check 'dial up networking'.
your phone should show up as '/dev/cu.usbmodemsomenumber'. i think this number is autogenerated depending on how many times you plug it into your mac whilst in dial up networking mode, because the first time i tried to tether over usb, it assigned it the number 411. its now 621. anyway, that doesn't really matter...what matters is that it has a /dev/ entry and that the user can actually access it.
step two: set the modem up under os x:
the password is your phone number.
step three: configure the modem type:
by default, the modem type will be apple v.32, which is a fail. set it to generic. the rest of the settings just make sense. i didn't play around with them, but it worked for me.
remember to uncheck the dial up networking box when done.