Integrate Windows application into ASP.Net Web application

Answer: Though Web.

1. Expose a Web Service in ASP.Net application

2. Call it in Desktop as well as Mobile application

http://support.microsoft.com/kb/818364

http://www.codeproject.com/Articles/26941/Consuming-Webservice-In-A-Windows-Application

http://www.codeproject.com/Articles/26941/Consuming-Webservice-In-A-Windows-Application