The Blackberry Messenger (BBM) app is to be offered as a download to run on rival platforms.
Blackberry said it would initially offer texts, photo
messages and group sharing functions on devices running Google's Android
and Apple's iOS operating systems from "the summer".It added it planned to roll out screen sharing, voice and video calls - all without charge - later in the year.
The move could prove disruptive to Skype, Whatsapp and other rivals.
Blackberry chief executive Thorsten Heins revealed the surprise news at the end of his presentation at the firm's annual developers conference in Orlando, Florida.
The company said that more than 60 million Blackberry owners already used BBM at least once a month.
But Mr Heins played down the idea that offering the feature to rival devices would harm sales of the Canadian company's own handsets.
"You might ask the question why is Blackberry doing this now," said Mr Heins.
