Hi Andrei After 3 year !! 
I want develop a C# app for the handheld scanner and a Web Service as a middle-ware between SAP and the Scanner on windows mobile 6.1 and read / write direct to sap .. I use Sap web service on windows app(Create an SAP Web Service, Call Web Service from .Net Application, Passing User Credentials) but when I create device App I cant use this please tell me How i can do this?