I received following question:

Answer:
Specific of Virtual Service Desk is that personnel is geographically dispersed and that they can be organized in various ways. That also provides options for measuring e.g. telecommunication costs, dropped calls, number of resolved incidents (or other calls) per group (if they are located e.g. on same location), availability of agents (e.g. if they work from home or office that is not supervised), etc.
Of course, all usual measurements related to the Service Desk apply also. This articles can give you idea:
ITIL Service Desk types https://advisera.com/20000academy/blog/2014/05/06/itil-service-desk-types/
Service Desk: Single point of contact https://advisera.com/20000academy/knowledgebase/service-desk-single-point-contact/