If you use the latest raspberry-asterisk OS, you can have chan_dongle available. I have made it work with my USB stick. Then it should be ok for in and out. However, I am not ok with the freepbx and never have time to properly configure.
Furthermore, if I have 3G/4G smartphone(with dataplan), I need only one OBI110 by installing OBITALK.
柬埔寨手機 <----> 柬埔寨landline--->柬埔寨OBI110<---->Intenet<----> 德國OBITALK