Update custom field(choice type) in Discussion list while creating a Threaded Discussion using List.AddDiscussionBoardItem Sharepoint WebService

Question

I'm trying to create a new threaded discussion to sharepoint Discussion board using Sharepoint WebService AddDiscussionBoardItem using the code from below link

http://social.msdn.microsoft.com/Forums/sharepoint/en-US/25d55767-71f1-4e1a-a62e-8a22f9de58a8/adddiscussionboarditem?forum=sharepointdevelopmentlegacy

The item is created successfully with the given subject, thread index and body. But the custom field (choice type) is taking the default value given while creating the list rather than the value passed.

Please suggest how to update the custom field along with subject and body using AddDiscussionBoardItem WebService.