As Facebook's (NASDAQ:FB) $19 billion acquisition of WhatsApp proved in February, there's plenty of value to be had in a good mobile messaging platform. But what happens if that platform can't maintain its growth?

According to the Fool's Steve Symington in the video below, that's the problem BlackBerry Ltd's (NYSE:BB) BBM platform is currently facing. Specifically, after boasting in late October when BBM gained 20 million new users in its first week as an available download for iOS and Android, BlackBerry management just confirmed BBM currently has "just" 85 million monthly active users -- good for an average gain of roughly 1 million new users per month since then.

That might sound good, but consider the fact in the five months leading up to its acquisition by Facebook, WhatsApp grew from roughly 250 million monthly active users to 450 million. When Facebook announced the agreement, it stated WhatsApp was still adding around 1 million new registered users per day.

Steve also points out BlackBerry management claims to have a "very solid BBM monetization plan" in place, with plans to further grow its user base in part through its inclusion in the Nokia X platform, Windows phones, and with its enterprise centric versions of the software. But will that be enough given the absence of meaningful growth going forward? To hear Steve's full take on what this means for BBM, check out the video below.