Some calls go straight to voice mail, others don't. Seems to happen randomly.
Some calls go straight to voice mail, even when no call handling rules are set up to do that. Other calls ring normally. Seems to happen randomly, and many times per day. The phone begins to ring for just a fraction of a second, and does not forward around the office as our rules specify. Customers say the phone doesn't ring at all and goes straight to voice mail.
I've cleared this issue with my client (cab company that has high call volumes).
Replaced a Cisco small business router rvs4000 with an ASUS RT-N66u (much more stable router)
Replaced a Dlink switch with a Netgear Prosafe GS724TP 24 Port PoE Switch.
No more problems.
We have the same issue with three smartphones using the app, so ours is not a router issue. I wouldn't think it was a bandwidth issue either because I had 4G service when one client failed to get through twice in a row.