I need some advice here. I am looking for an app that both Blackberry and Iphone support that has a good service for instant messaging? What have you used that would work? BBM was my favorite and now I have the Iphone I still want to stay in touch with my Blackberry users.
nimbuzz
Thanks man! have you used this with either device before?
Nope! 
But I used it on Symbian, and any app that works worth a damn on Symbian will work well with a real OS. It does facebook chat, google talk, aim, skype chat, and other shit that I don’t have accounts for.
Not free, but BeeJive IM
google talk
cant you just get the msn messenger app?
or yahoo talk?
there are dozens of these apps out there isnt there?
why not just text message 
I prefer IM+ on iPhone, there is a free ‘lite’ version that works well.