Thanks Ido.
With inspiration from your post, I tried the hostname you mentioned. It failed at   $yahoo->login or die "Can't login Yahoo!Messenger";
I scanned the registry under Yahoo IM and found the entry for hostname as  'scs.msg.yahoo.com' However, it still fails to login, although it makes  Net::YahooMessenger->new connection.
Note:
Iam able to login with the same userid/password from actual yahoo messenger client.