On selecting New , you will be presented with the following screen.

Here the debtor can be specified by typing first few characters which will bring up a list. Choose correct debtor/customer. If a Caller is linked to the debtor, by typing first few characters of his name in caller tab, it will show in list which you can sellect. Fill in description of the call. If call needs to be linked to an existing quote or jobcard, please specify accordingly.
Priority, Status and Incident must be set accordingly. Incident Type is required and will Determine if a JobCard is generated or not. Technician can be captured by entering first few characters of the name. File can be attached as well with info relating to the call.
If your system is set to close Service Desk Calls based on JobCard being Closed this will use the System User to Complete these Calls.
