Today I've came across this post, it clearly shows how some smartphones are losing market participation while others are increasing sells.
As the author of the post states, that is tied to the platform each manufacturer decided to use and more and more people are going to Android and iOS while leaving Symbian and Blackberry OS.
I've owned an E71 and E72, also and Android phone and a Blackberry and I must say that the decision of which one to choose should be given by your individual needs.
What I mean is: If you really need all the fancy apps that comes with iPhone and Android phones, but you do not care to much about battery life and you can afford suddenly loosing your phone at 8 o'clock in the night while still out in meetings or whatever you are doing, the you can go and get one of those, they clearly do a lot more things than Blackberry.
But, if you need to stay on line all day long and you do not have time to run to a power outlet before you arrive home late at night, then you must stay with Blackberry.
There are lots of apps for Android that disconnect your phone from the network or turn WiFi off, just to make your battery last a little bit more, also a lot of recommendations for the same thing with iPhones, I have my Blackberry 9780 connected to the network and with WiFi on all day long getting emails, and it last at least two complete days without a charge.
So, do not let the tendencies guide you, decide by yourself based on your needs.