I have used something like this hope it helps
// cyberlogicserver is the web service in my web reference
// webserver var stores the URL read from app.config or any INI file or
// xml file
cyberlogicserver cyberlogicwebservice = new cyberlogicserver();
cyberlogicwebservice.Url = "http://"+WebServer+"/cyberlogicserver/cyberlogicserver.asmx";
cyberlogicwebservice.Credentials = System.Net.CredentialCache.DefaultCredentials ;

try
{
// my actual web service call
DataServer = cyberlogicwebservice.activatecompany(ActivationKey,ComputerIpAddress);
}
catch(Exception e)
{
MessageBox.Show("There was en error communicatioing."+e.Message , "Error Activating Company" ,MessageBoxButtons.OK,MessageBoxIcon.Stop);
oForm.Close();
return;

}

>Hi,
>I have web services sold to couples of customer. Of course, they would have own ISP/Web Server, with different URL. My question is, how could I call the SAME web services from my client app which hosted in difference web site without I change my project web reference everytime?
>
>Thank you