Toronto - BlackBerry Ltd said on Wednesday that its popular BlackBerry Messenger instant chat application will be available for rival devices using Google Inc's Android software and for Apple's iPhone this weekend.

The struggling Canadian smartphone maker had announced plans to open up the service, often referred to as BBM by both fans and the company, back in May.

Once a unique tool to send short messages without running up SMS charges, BBM now competes with mobile instant messaging products from Facebook, Apple and others, and less directly with the micro-blogging service Twitter.

Android users will be able to download the application on Saturday, while iPhone users can get it on Sunday.