This article explains how to add a ringtone to your Grandstream DECT IP Phones. The same process can be adopted for other Grandstream Desk Phones as well.
Download a suitable ringtone (must be .WAV format, MP3 files will need to be converted before continuing):
Download and run the Ringtone Generator from here to generate a ring1.bin file:
Download Tftpd64 Portable Edition from here and set your directory, server interface and check the show dir to ensure your ring1.bin file is inside your tftp directory:
Set your base station / phone firmware server path to the IP Address of your TFTP server and ensure the Upgrade via is set to TFTP. Save and Apply, then reboot your device.
Verify the device picks up the ringtone:
Once the device has rebooted and downloaded the ringtone, login to the device and navigate to DECT Handset Settings > HS1 Settings and change the Custom Ringtone to ring1.bin: