Switchvox - How do I set the idle screen on multiple Sangoma phones?

Select the Setup tab and choose Manage under the Extensions section.
Click the Bulk Modify Extensions button.
Select the Sangoma Phones tab under Phone Settings.
Choose the Idle Screen dropdown and navigate down to the Idle Screen section then select the Upload Picture icon.
An idle screen image logo must be a PNG image. The optimum dimensions are 205x85 but any image size can be accepted and scaled.

You may have to reboot the phones. If you are still seeing the Sangoma Logo on the screens, it is likely that your firewall is not allowing traffic to the server over ports:

443 UDP: Switchvox API (used for Sangoma Phones only*)
80 UDP: Phone firmware updates (used for Sangoma phones only*)
5062 UDP: SIP (used for Sangoma Phones only, and only when used with Switchvox versions lower than v6.4. This port is not used by Switchvox x6.4 and greater*)

Your firewall would have to be configured to open those ports to the Switchvox server IP address.