How to call a web service using HttpWebRequest

Question

I am able to successfully retrieve the wsdl from a server with the code below.

How can I now call a method (GetVersion) from this same service?

Trying http://www.servername.com/DataService.asmx/GetVersion returns an error saying the page cannot be found. I have no problem calling the method from a .Net WebService reference, but I'd like to be able to use an HttpWebRequest.

Dim req As HttpWebRequest
Dim resp As HttpWebResponse
Dim sr As IO.StreamReader

req = WebRequest.Create("http://www.servername.com/DataService.asmx?wsdl")
resp = req.GetResponse

sr = New IO.StreamReader(resp.GetResponseStream)
txt.Text = sr.ReadToEnd
sr.Close()