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 #

To set the phone back to "Admin mode", press the Settings key:

Firmware versions lower than 7.X: Select "Admin Mode".
Firmware versions lower equal or greater 7.X: Enter "Maintenance" and select "Admin Mode".
On the prompt enter your administrator password, if you have set one, or the default password, which is "0000" (four zeros), and confirm.

Reset lost administrator password by performing a 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.