Virtually all VoIP phone systems use the Internet for communication, and are just as subject to h hacks and attacks as computers and workstations. You can take the following measures to secure your VoIP phone system: Avoid “punching holes” (port forwarding) in the firewall to allow VoIP providers to manage the phone system. Instead, consider placing all the phones on a separate VLAN (automatically done if VoIP QoS is enabled on the Uplevel system) and creating a remote access VPN account that has access to this VLAN.
Enable strong firewall protections such as Threat Analysis and Country Blocking - in particular, block off unwanted countries that are vectors for attacks. Place the phones on a separate VLAN, as mentioned above, with no other devices such as workstations or servers on this VLAN.
If an on-premises VoIP server is present, audit the configuration of the VoIP server to ensure that no security holes are inadvertently created. VoIP servers are designed to maintain high voice quality, and frequently do not pay a lot of attention to network security.