Switchvox - How do I correct the date & time on my Sangoma phone when my System Clock is correct?

First reset the phone to factory defaults:

Press the More... softkey until you see the Menu softkey on the bottom of the phone's display screen.
Press the Menu softkey.
Press 5 on your dial pad, followed by 2.
Your phone has been reset back to its factory default. If the date and time is still not correct follow the next steps.

Next, setup the Phone Network to have an NTP Server of the internal IP Address of the Sangoma PBX server instead of http://0.digium.pool.ntp.org The internal IP Address can be found under Server > IP Configuration > eth0 Interface > IP Address.

Navigate to Server > Networking > Phone networks.
Locate the network you want to change and Modify (click the yellow pencil).
Enter the IP address of the server (internal if the phones are on the same subnet) in NTP Server field.
Reboot the phone by unplugging it and plugging it back in again.

If the time on the phone is still incorrect, log in to the DHCP server that the phones are accessing to get their IP Address assigned. That may be a router, or another server on the local network used as a DHCP server. Check the settings on the DHCP server to make sure the NTP Option is not enabled (even if there is no server specified in the setting). If it is enabled, disable it and then reboot the phones. The time on the phone should update to the correct time. Sometimes, it is necessary to force the DHCP server to renew the phone's DHCP lease in order to update the time.