Don't be fooled by that app. They're attempting to lock you into a locked in device. There are already plenty of free ways to contact iPhoners, mainly using IM protocols like MSN Live, Yahoo Messenger, AIM, Jabber/GTalk, and others. These are available on the iPhone, and free and included in the N900 out of the box. Don't let BB Messenger and Whatsapp suck you into long term bouts of wasting money. Go with what has worked all along.