MacRumors reporting on the gradual release of BBM after a previous aborted launch:
To avoid similar issues with strong demand this time around, BlackBerry is using a staggered queue system to handle the demand. Users will install the app, enter their email address to hold their spot in line, and then will receive an email when they can start using BBM.
Demand? Are there seriously any iOS users out there who are thinking “Man, I wish I had a way of communicating with the only friend I have who owns a Blackberry that isn’t SMS or email”?