Currently, there is a line up system, most likely to alleviate pressure on their servers. People who have signed up on BlackBerry's website before to get BBM get instant access now.
For others, there is no indication when it will be available. There are also many reports of difficulties using the BlackBerry ID sign up on mobile devices. We suggest signing up on a computer at this link so you can start using BBM once it is available to you.
Get it now on the Play Store and on the App Store.
To learn (or relearn) how to use BBM, BlackBerry has released many informative tutorials on using BBM.
Watch them below!