Please note that there is support for a "received message" popup, but not an icon. This popup is turned off by default, however. You can find it by opening the Conversation App (not just an IM or SMS conversation), opening the app menu, going to Options or Settings (whichever is the translation, it's called 'instellingen' in Dutch) and turn the feature on.

This is a small argument for a telepathy plugin, but tgalal already mentioned his plans for that plugin if I'm not mistaken.

Tgalal, what language are you writing this app in? And I heard that the hashing of the password happens at the client side, that opens the door to user-chosen passwords? (just checking, there has been some mentioning of this). Did you take a look at code which implements a non simcard way? I'm not too fond of some company having my mobile phone number... There has been some mentioning about privacy issues regarding Whatsapp, especially regarding the sending of the entire contacts database. How will you cope with that?

I'm looking forward to the app, but looking even more forward to the telepathy plugin. I wish I could help Placing the code on some repository opens the door to help, but of course that leads to all kinds of unwanted side-effects (such as an other publishing the app and what not) so I respect and understand your decision.