Sound
You can use different ringtones to differentiate the incoming calls and notifications.
These ringtones can be assigned to the different call types, identities and callers (if set up as a contact). You can make these assignments depending on which information you think is the most important. Configure the required settings as follows.
*Further help under Contacts
*Further help under Identities
Priority for defining ringtones 
The phone checks the existing ringtone settings for incoming calls and determines the ringtone used based on the following order.
1.Contact ringtone (the telephone number of the caller is checked)
2.Ringtone that can be downloaded externally via a valid URL (the alert info in the SIP Invite is checked)
3.Ringtone by call type (the alert info in the SIP Invite is checked)
4.Identity ringtone
5.Default ringtone
6.Android fallback ringtone
Ringtones by call type 
The ringtones available in the phone can be assigned to different call types using an alert info in SIP Invite. This allows, for example, different call types such as internal, external, group and door calls to be distinguished by different ring tones when operating on a PBX.
By default, six search terms are already predefined in the list of call types.
extern for external calls
intern for internal calls
group for group calls
door for door calls
alarm for alarm calls
silent for silent calls
Depending on the support of the PBX or the provider, further search terms can be added to the list, for example:
group-123 for calls to the group number 123
external-911977 for calls to the external number 911977
door-511 for calls from the door 51, door bell button 1
The list is completely evaluated during a call in order to determine search terms that match the alert info. If there are several matches, the entry with the longest search term is used.
Exception: If a matching search term is found with RegExp expressions, the associated ringtone is preferred.
Own ringtones 
Additional ringtones can be added to the device. The number of ringtones is only limited by the amount of memory.
Supported file formats:
.wav
.mp3
.ogg.
Maximum music file size: 5 MB.
*Important: Personalised ringtones will not be backed up.
*Further help under Backup and restore
Handset sidetone 
To enable a better sound experience during a conversation at the handset, a sidetone is played in the handset as standard. The sidetone is an audible feedback indicating an active transmission. A lack of sidetone, for example, can lead to speaking too loudly.
This deliberate feedback can interfere with loud ambient noise. In permanently noisy environments, it therefore makes sense to switch off the sidetone.
Configuration
*Note: The following restrictions apply when setting up:
Only on the phone: Setting default ringtones, listening to ringtones, changing the volume.
Only in the web interface: Importing and managing your own ringtones
Web interface: 
Sound
*Description of the operation under Sound
Phone: 
Settings > Sound
*Description of the operation under Sound
Provisioning: 
*Details about provisioning this function in the Auerswald DokuWiki
Video: Setting up call type-dependent ringtones 
*Link to video (only in German) https://www.youtube.com/watch?v=rgZLN7u7jEU
Video: Setting up own ringtones 
*Link to video (only in German) https://www.youtube.com/watch?v=DtrNdzMUOBQ