Cnn.com gives a very good overview of why the BlackBerry is so popular and how it has evolved.
Cnn writes People don’t just use BlackBerry; once they’ve discovered it, they can’t live without it. Though it can be used as a phone, the BlackBerry’s power lies in its ability to push e-mail automatically from the company server to the end user. That simple concept has revolutionized corporate life. Two million BlackBerry subscribers have already signed up and their numbers are growing rapidly. You might perhaps expect that the must-have executive gadget was unleashed on the world from somewhere inside one of the high-tech hothouses of Silicon Valley.
Although RIM’s BlackBerry can be a phone and an email device most busininesses rely on it primarily for its powerful email features.