Aastra SIP 53I Administrator's Manual page 385

Configuring Operational Features
Operational Features
When you download the Callers List, the phone stores the callerlist.csv file to
your computer in comma-separated value (CSV) format.
You can use any spreadsheet application to open the file for viewing. The
following is an example of a Callers List in a spreadsheet application.
The file displays the name, phone number, and the line that the call came in on.
41-001160-00, Release 2.1, Rev 04 5-175