Whatsapp appears to use XMPP (Jabber), but on Whatapp's own, closed servers. Were the company to allow access by third-party clients, the N900 would have everything needed already. Or, if Whatsapp were an open source app, it would likely be ported already.

Instead, Whatsapp is a closed app on a closed XMPP network. As such, it's up to the Whatsapp company to write a Maemo 5 client. They've stated they have no intention to do so, so the matter rests.

Complaining and wishing here won't help. Admittedly, complaining and wishing to Whatsapp, Inc. almost certainly won't help either.