The option of making anonymous calls can be easily activated and deactivated in my edpnet:
1. Go to my edpnet.
2. Choose My Configuration → My Telephony.
3. Click on the Edit icon:
4. Click on the telephone icon under the option "Show my number"
If the option is inactive, you will see . Click on this icon if you intend to make anonymous calls.
If the option is active, you will see . Click on this icon if you want your number to be identified.
If would like to make a single anonymous call
If you need to make just one anonymous call, you can simply use the prefix #31# that will tell our telephony servers to not display your phone number. Example: #31#081234567.
If your telephony is configured on a FRITZ!Box, you should also add *# before the code in order to prevent the modem from intercepting the request. Example: *##31#081234567.