Is it safe to switch a .NET 1.1 webservice to a WCF service, knowing that not all clients use .NET to access the service? So they use the SOAP/XML method. Can we switch to WCF without the clients having to change code?
Yes. While I haven't done it with a 1.1 web service, I was able to refactor a .NET 2.0 webservice into a WCF service, then just expose it with basicHttpBinding. The client didn't even know the difference.
I dug through some of my saved links when I was working on it, and this blog and a good msdn article were what got me started. Really simple and to the point.