public override int IndexOf(PhoneNumber x)
            {
                int result = 0;

                rwLock.AcquireReaderLock(timeout);

                try
                {
                    result = collection.IndexOf(x);
                }
                finally
                {
                    rwLock.ReleaseReaderLock();
                }

                return(result);
            }
 public override int IndexOf(PhoneNumber x)
 {
     return(m_collection.IndexOf(x));
 }