i have this strange issue with our gxp1625 we have an allworx setup with this phone as a sip. i can make calls and receive calls fine.
however i cant use our paging system with it. when we dial the paging extension. (bogen tpu-35b) i hear the tone. in the handset and pa speakers. but i cant say anything. almost as if im muted. we tried using a pc based sip client (zoiper) and that works fine. and also all the phones on our analog phone gateway work fine with it.

my guess its a setting on the phone but not sure what one to change.