Activate PBX for the user you want to test with. In this example I set extension 14 for admin user (userid=1):

UPDATE `vtiger_asteriskextensions` SET `asterisk_extension`='14', `use_asterisk` = '1'
 WHERE `vtiger_asteriskextensions`.`userid` = 1;

Once you do that, reload the coreBOS page and open the inspector network tab. You will see that asterisk.js has been loaded and that the polling has started.

Now we insert a call directly in the DB:

INSERT INTO `vtiger_asteriskincomingcalls`
 (`from_number`, `from_name`, `to_number`, `callertype`, `flag`, `timer`, `refuid`)
 VALUES
 ('03-3608-5660', 'joeb', '14', 'SIP', '0', UNIX_TIMESTAMP(), 'any_unique_id');