The various IM apps around make BBM look irrelevant. Why? BBM is only
limited to blackberry phones and you can’t use it without a BB PIN (
Blackberry Prisoner Identification Number) but these alternatives work across all platforms.

Skype is probably the most popular IM application and as a matter of
fact, it’s more than just an instant messaging app. With Skype, you can
keep in touch with family and friends and it supports video calls on
almost all mobile platforms except, of course, the overrated Blackberry.
Even Blackberry’s most sophisticated smartphone doesn’t support video
calls on skype for now.
Skype to Skype calls are free and you may even buy call credits at a very reduced rate.
I’m not the chit-chat type that spends the whole time chatting with
people on social networks but Whatsapp really got me. With over 100
contacts on my phone already using it, it’s probably the best
alternative to Blackberry messenger since it consumers very little data
and it works across all platforms. Even almost all BBM users have
Whatsapp installed on their device to keep in touch with their contacts
who do not have that thing they call Blackberry PIN.

Although the latest blackberry messenger can make voice calls over Wi-Fi
which is quite a big step forward for the company and something very
appreciated by all BBM users to say the least, I’ve been doing that with
Viber and Skype for a very long time over 3G. Viber is very widely used
and also, the free VoIP feature is great.

This doesn’t need an introduction and you definitely can’t deny the
fact that Facebook is the largest social network right now and when it
comes to instant messaging, Facebook chat has a lot more users than any
other IM application. There’s a Facebook messenger for every phone, even
feature phones.
Compared to others, I use this a lot less but it’s a great instant messaging app with a cool UI.
You got a lot of alternatives and the choice is yours. I have most of
these installed on my iPhone and Nokia N97 and I still keep in touch
with my loved ones. Not sure I’m gonna get a Blackberry device just
because of BBM…