Here's how to Factory Reset your VoIP Phone:

Snom 3xx Series

Since firmware version 8.7.3.7 on the Snom 3xx Series it is possible to reset the phone using the key pad by pressing the following key sequence:

* Volume Up * Volume Down #

Reset to factory defaults via Phone Interface:

Snom 300 - Enter the "Settings" menu, enter the "Configuration" menu, scroll down to "Reset", press "Confirm" button (looks like a tick), then press soft button under "Reset" on display.
Snom 320 - Enter the "Settings" menu, enter the "Configuration" menu, scroll down to "Reset", press "Confirm" button (looks like a tick), then press soft button under "Reset" on display.
Snom 360 - Enter the "Maintenance" menu, scroll down to "Reset Values", press "Confirm" button (looks like a tick).
Snom 370 - Enter the "Maintenance" menu, scroll down to "Reset Values", press "Confirm" button (looks like a tick).

Reset to factory defaults via Web User Interface:

Obtain your phone's IP address and currently used firmware version by pressing the Help button on your Snom 3xx.
Open any web browser and choose the URL corresponding to your current firmware version:
- Firmware versions lower than 3.X - http://1.2.3.4/set_base_en.htm?reset=Reset
- Firmware versions between 3.X and 6.X - http://1.2.3.4/advanced.htm?reset=Reset
- Firmware versions from 7.X onwards - http://1.2.3.4/advanced_network.htm?reset=Reset
Copy the appropriate URL into the address line of your web browser and then change "1.2.3.4" to your phone's actual IP address.
The phone reboots automatically and everything will be accessible again.