It looks like apple has let you (re)add your own custom ringtones with iPhone firmware 1.1.2
Just take your m4a file, and rename it to a m4r, double click it, and it should open in iTunes, then you can sync them to your iPhone again!
Thank You Apple!

Just take your m4a file, and rename it to a m4r, double click it, and it should open in iTunes, then you can sync them to your iPhone again!
Thank You Apple!