We just had a situation where our Panasonic home-phone-and-answering-machine would ring but the answering machine would not pick up nor would we get the voipo voicemail. Folks called us on our cell to let us know our home phone wasn't working properly this afternoon and evening.

Tonight I rebooted our Grandstream and then called home. The home phone knew who was calling with caller id, and displayed "Answering" on the display but for some reason the answering machine was bypassed and the call went immediately to voipo voicemail and I got an email with the message from voipo.

Turned the phone/answeringmachine off and on. Called home, the home phone/answering machine correctly answered and saved the message rather than shunting directly to voipo voicemail.

So...it appears that once things get in a funky state it makes sense to reboot your Grandstream and then your phone.

FWIW