VICIdial APIs are limited and provide API to initiate a call. So to get the complete information of the call, Vtiger has a CRON service running in the back end every 30 min.
On every CRON run, Vtiger fetches call record information from 100 records (maximum) and updates corresponding call records to 'completed' status.
To learn more about VICIdial integration,
click here.
To learn more about the Phone Calls module in Vtiger,
click here.