BlackBerry has just announced that its BlackBerry Messenger service will be released for Android and iOS as a free app this summer. That's a major strategy shift for the company, which has long touted BBM as a key advantage of its platform – and indeed it's been one of the main reasons why longtime users were clinging on to their BlackBerry smartphones. But while the move has been clamored for years, the company's response comes at a time third-party cross-platform messaging apps like WhatsApp have already taken off.

Whether this will be a case of too little, too late remains to be seen. CEO Thorsten Heins claims the time is just right "to bring BBM to a greater audience," but investors are probably feeling a little uneasy as evidenced by a 6% drop in BlackBerry's share price, the biggest decline in a month after the renewed optimism brought by BB10.

BBM will be available as a text-only service on rival platforms in the next few months, subject to approval by Google Play and the Apple App Store, with voice and screen sharing to be added further down the road.

The messaging service currently has more than 60 million users, who send and receive some 10 billion messages every day. Opening up to other platforms will certainly help that figure grow, but that's still some ways off from overtaking current mobile messaging leader WhatsApp, which claims 200 million active users.

Others like Kik and Line are also seeing considerable growth, suggesting there's still room left for competition. Apple's iMessage might be a little limited but it works fine and comes pre-installed on millions of iDevices. And of course then there's, Google, which is expected to release its unified messaging service tomorrow.

It'll be interesting to see how this move plays out. Once the floodgates are open I very much doubt that BBM will serve as a hook to get new users on BlackBerry's platform. The company is probably hoping to retain current customers by giving them the ability to communicate with the growing pool of non-BlackBerry users within their preferred messaging app, but it might end up offering them just the incentive they need to jump ship.

In addition to making BBM cross-platform, BlackBerry announced BBM Channels, which sounds a lot like the company's version of Twitter. The new service will let users follow the brands and celebrities they're interested in to receive updates and create their own channels that other users can follow.