A day after BlackBerry finally managed to push its BBM for Android and BBM for iPhone apps out the door, WhatsApp fired a warning shot to remind the struggling smartphone vendor of what it’s up against. BlackBerry touted on its BBM Twitter account that it activated more than 5 million new BBM users on Android and the iPhone in less than 8 hours, which is certainly an impressive feat. WhatsApp, however, now has 350 million monthly active users. WhatsApp CEO Jan Koum made the announcement on stage during a keynote presentation at the Nokia World 2013 conference, and that figure is up substantially from the 300 million monthly active users WhatsApp had just over two months ago in August. As the cross-platform mobile messaging market becomes increasingly crowded, WhatsApp is showing no signs of slowing down despite its refusal to embrace the new revenue channels being exploited by rivals, such as mobile payments and gaming platforms.