"I wrote down the URL and in three days there were hundreds of people using it. Half the parts that we thought were essential didn't work but they could still use it, and they did."
And once it became popular, other employees had to join in to stay connected. "If someone on a team didn't want to use it, they found they had to because the team had started planning their monthly lunches on it," Klassen remembers.
He doesn't claim to have had a grand vision for BBM from day one, and certainly not a cross-platform one. "With technology, often we look back and say 'that's why we built it, we built it for this or that' - but sometimes you don't. The way that BBM came about was that we built something and we listened carefully to what stuck with the users."
Giving in or spreading out?
BBM has always been one of the selling points for BlackBerry, so is bringing it to iOS and Android an admission of failure? CEO Thorsten Heins said repeatedly at BlackBerry Live that taking BBM cross-platform now is a vote of confidence in how good BlackBerry 10 is and how many features it has beyond BBM.
As Bocking pointed out to TechRadar, it could be an advert for BlackBerry. "Going cross-platform; think about what an opportunity that creates for people to experience BlackBerry Messenger and get a taste for BlackBerry. We can turn 60 million BBM users into advocates on social networks."
Klassen agrees that it's far easier for people to see the appeal of BBM once they've used it. "There are people, when I talk about Ds and Rs, who have stories about what that has meant to them. If I talk to someone who hasn't used it before, their eyes glaze over. They don't understand the benefit and it's hard to explain that you get addicted to looking for the R until you've experienced it.
"We're giving people the opportunity to experience it and then they can ask themselves 'what is it about this that I like?' And then maybe they'll ask 'why is somebody in my community [who's using a BlackBerry] able to communicate so much more effectively?'"
But there is another reason. With BBM Channels launching, BlackBerry needs to have as many users as possible for brands to sign up to their channels so BlackBerry can earn money from things like sponsored invitations.
As Bocking explains, "Extending [across other mobile platforms] grows the audience, and a large base is critical to have the mass to monetise any service.
"Going cross-platform is an acknowledgement this is a heterogeneous environment we are living in, and by supporting our services across those platforms we can support our customers, [something] they've asked for."
That means BBM has to be as good on iOS and Android devices as it is on BlackBerrys. It will start with text and images but voice and video chat will come later. "We want feature parity so we can build a highly engaged audience on the platform," says Bocking.
And Klassen told us that includes core features. "We can implement the same user interface and we can tell you when a message has been delivered. Those things will be built in, so we can give you the same confidence you're looking for when you send a message."
BBM isn't coming to Windows Phone this summer, but that's not because Microsoft is the competition, says Bocking. "Our users have been focused on asking for iOS and Android; we have not been hearing requests for Windows Phone.
"I won't say that will never happen. It's a matter of is there interest from our users, if they are asking for it. Equally, we don't have plans for a web-based client, but we'll be listening to what our users want."