web service - Use the MessageName property of the WebMethod custom attribute to specify unique message names for the methods

Step 1: Use diffrent MessageName attribute values.

public class MyWS : System.Web.Services.WebService
{
[WebMethod(MessageName = "GetItemById")]
public Item GetItem(int id)
{
...
}

[WebMethod(MessageName = "GetItemByUniqueTitle")]
public Item GetItem(string uniqueTitle)
{
...
}
}

Step 2: Set your webservice binding: ConformsTo = WsiProfiles.None