Starting from firmware version 184.108.40.206, all Snom Desktop phones equipped with a USB port can store SIP traces on a mass-storage device. In this case the trace size is limited to the USB device free space only.
In order to enable this feature you need to:
Enable the usb_storage_siptrace: you can do it via provisioning or via phone web interface clicking on Advanced -> QoS/Security
Unzip and save the "flag file" siptrace.flg into the USB stick root directory
Plug the USB device into the phone USB port, the phone should detect the storage device
At this point the phone starts saving the sip trace on the USB device, once you reproduced the issue you can unmount and unplug the USB device. Un-mounting the device before unplugging is fundamental in order to avoid data corruptions, the USB device can be un-mounted pressing the Menu key, selecting Maintenance and then Unmount USB disk: