It's similar to sending it from the web service to the client.  Make sure
you modify the proxy class so that it derives from
Microsoft.Web.Services.WebServicesClientProtocol.

Client:
           // Create instance of web service
           wsUpload = new WSUpload.WSUpload();

           // Create attachment from posted file stream
           DimeAttachment da = new DimeAttachment("plain/text; charset=
utf-8",
                       TypeFormatEnum.MediaType,
hifUpload.PostedFile.InputStream);

           // Add it and send it to the server
           wsUpload.RequestSoapContext.Attachments.Add(da);

           wsUpload.TransferFile();

Server:
           // Get the stream and do something with it
           StreamReader sr = new StreamReader(
               HttpSoapContext.RequestContext.Attachments[0].Stream);