BlackBerry Ltd said it will make its messaging service BBM available to Microsoft's Windows Phone and the upcoming Nokia X platforms in the coming months.

BlackBerry Messaging, or BBM, is a messaging platform that offers collaboration tools such as BBM Groups, BBM Voice and BBM Channels and competes with services such as WhatsApp, which Facebook bought last week for $19 billion.

BBM will be available as a free download from the Windows Phone Store this summer, while BBM for Nokia X will be available from the Nokia Store when the Nokia X platform launches, BlackBerry said in a statement on Monday.

BBM was a pioneering mobile-messaging service, but its user base has failed to keep pace with that of WhatsApp and other upstarts, in part because BlackBerry had long refused to open the service to users on other platforms.

WhatsApp, with a user base of about 450 million, on the other hand has grown rapidly. Its service works on Apple Inc's iOS platform, Google Inc's market-dominating Android operating system and with devices powered by both the Windows and BlackBerry operating systems.

BBM remains popular, even though BlackBerry devices have waned in popularity. Late last year, the Waterloo, Ontario-based company finally opened the messaging platform to users of iPhones and Android devices, and the number of the service's active users has grown to more than 80 million.