Customer is unable to receive inbound calls.
This is related to the IP Handsets ability to register to Gazelles network. There are a few possibilities:
1. Power Outages
2. Loss of Internet Connectivity
3. Router / Firewall security options are blocking VOIP traffic.
Note: Calls should still route to Auto Attendent and/or VM. Customer can also choose emergency routing options, i.e. route to cellular phones.