in your code:
YourWebService.Url = ConfigurationSettings.AppSettings["wsURL"];
also
"Simply choose the properties of the web service and change the "Url Behavior" from "Static" to "Dynamic". This will automatically create an entry in the <appSettings> section of the Web.Config file that contains the Url string. The constructor of the Web Service proxy class is automatically changed to set the Url property to the value stored in Web.Config.
"
see
Setting Web Service References Dynamically
http://www.aspalliance.com/shark/articles/WSDL/Wsdl.aspx