Trapping a client timeout in a webservice method

[MrXLand]

I am trying to find out how to trap a client timeout within a webservice method call.

I have a particular webservice method which does several things. The first thing it does it create a unique reference and what I want to be able to do is return it to the client if the method timesout because it is stuck in a subsequent part of the call. A try {} catch {} on the server doesn't seem to be invoked when the client call times out. Is there some other way of trapping that or do I have to go down the route of separating the server parts into separate webmethods?

e.g. In summary:

CLIENT CODE
try {
  string response = ServerCall();
} catch (Exception e) {
  // This is part is invoked when the time out occurs
}

---
SERVER CODE
[WebMethod]
public string ServerCall() {
  string myID = String.Empty;

  try {
    myID = Part1GenerateUniqueID();
     System.Threading.Thread.Sleep(600000);
     Part2DoMoreStuff();
     return myID; 
  } catch (Exception e) {
    // This is never called when the webmethod times out
      return myID;
  }