call_waiting_query
Description:
[ Version ( since = "1.12" ) ]
public async bool call_waiting_query (Cancellable? cancellable) throws Error
  public async bool call_waiting_query (Cancellable? cancellable) throws Error
Asynchronously queries the status of the call waiting network service.
When the operation is finished, callback will be invoked in the thread-default main loop of the thread you are calling this
      method from. You can then call call_waiting_query.end to get the result of the operation.
See call_waiting_query_sync for the synchronous, blocking version of this method.
Parameters:
| this | A ModemVoice. | 
| cancellable | A Cancellable or  | 
| callback | A TaskReadyCallback to call when the request is satisfied or  | 
| user_data | User data to pass to  |