Since version 1, ASP.NET has supported web services via the ASMX files. With .NET 3.0 and the Windows Communication Foundation (WCF), you have an entirely new way to expose and consume web services. So do you convert to WCF or leave everything as ASMX?
Starting with a preexisting ASMX-based web service, Thom Robbins shows how to add the necessary contract information to use the ASMX service as a WCF end point. The end result is a dual-mode service that can handle both traditional web service and WCF requests.
The lengthy instructions do raise the question, "Is WCF too complex?" If ASMX-based web services just work, why would you want to take the extra effort to develop a WCF solution?
Microsoft often touts the somewhat debatable advantages of a unified programming model, as well as advances in security and transactional integrity. When questioned about the latter, Thom Robbins offered the MSDN article, What is the Windows Communication Foundation?, as a starting point.