How can you set up the service desk to allow the assignment of calls to external 3rd parties

How can you set up the service desk to allow the assignment of calls to external 3rd parties

We work with external support parties; how can we set up the service desk to allow calls to be assigned to these external support without haveing to use up a technicians licence.
 
I would also like to be able to send a call close notification to the external support every time our technicians close a call they have been assigned.
 
Just now we have created 2 fields for the 3rd party name and 3rd party reference; and populate these, but the call is still assigned to one of our support technicians, so when the call is closed the 3rd party does not receive any notification of the close.

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