Outsourcing strategies of Mobile Network Operators (MNOs) have lead to the emergence of innovative business models, such as virtual operators. In this paper, we use literature review and multi case study analysis in order to analyze different elements of virtual operators and to identify standard types. The outcome is a categorization of virtual operators, which allows the standardization and structured comparison of any Mobile Virtual Network Operator (MVNO) business model. Based on this, we describe six virtual operators, which become accepted in the market: Branded Reseller, Service Provider, Enhanced Service Provider, full Mobile Virtual Network Operator, White Label Service Provider and Mobile Virtual Network Enabler. In addition, the categorization may also support virtual operators in defining and evaluating business models.