Had an issue with latest version of the 1.0.20-24 firmware if you don't have the
bindaddr = ipaddresstoasteriskserver
setup in sip.conf along with nat=0 canreinvite=no
you'll have issue on line 1 where you can hear audio but you can send out audio .
Versions prior to 1.0.15 where able to work around this but after the new updates it seems 1.0.24 requires you have this but i think its good to have this setup.