>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?

I also have a Web Service which is used on several servers. I never had to recompile the Web Service when we had to install on various servers. The only think we had similar to that is when we read a Main.ini file which resides in the same directory as the ASMX file to read the URL the Web Service is suppose to call to get its XML and the temporary directory.