Why Blackberry?

I have never understood why people may want to buy a Blackberry. People tell me it is the mail service, the others say messenger.

Does it really matter?

Now I have used a Blackberry in the past and use a handset even now. Blackberry service is more expensive than a normal GPRS service though it can be marginally be faster. Recently my employers provided me an HTC handset. I access my official and personal mails on that phone. Of course, both of them are Gmail service. It may be argued that the Blackberry service is the safest way to access emails using mobile service. But I am not sure if it sustainable advantage now. RIM started expanding its customer base and started targeting the youngsters and to me that segment may not be as worried as the corporate citizens about security. With iPhone and Android, RIM has also lost its the-email-phone status.

BBM is another app that is often cited for its success. But then with an app like Whatsapp, I am not sure if anyone needs a BBM like limited messenger.

Am I missing anything here? What is Blackberry's distinct competitive advantage? Someone please enlighten me.