Thought I would share this, as it has been a mission to work this out!
Using Visual Studio 2010, the test app uses the wsdl for querycustomerin. This done by: Add Service Reference > Advanced > Add Web Reference > URL = <Your WSDL link/file>, Web reference name = SAPQueryCustomerIn.
The test uses CustomerSelectionByIdentification > SelectionByBusinessPartnerName
Output is as so:
Source code is attached 😊