Yes we have a date for you now, you might want to check back 27th June 2013, thats the date BBM goes accross platform, read article about Blackberry's announcement to move the BlackBerry messanger to both iOS and Android powered devices

BBM on an iPhone (maybe prototype)

The announcement on Twitter by bbworldwid link here

Conversation on Blackberry's Twitter page concerning pricing

Pricing or access to this feature has not been made known as seen in the picture above

Will this development pull you away from popular instant messaging you currently use? like iMessage, Whatsapp, and Viber?

 Source | Source 1

This unit is now official but for developers