It sounds like you're considering an Android version of Blackberry Messenger (BBM). It'd be worthy to check out, I guess, but I'm pretty sure BBM runs, encrypted, on the RIM network. There is a reason Verizon has 2 data plans -- one for Blackberry and one for every other smart phone/device.
I'd venture to guess you're not the first one to think of bridging the gap. But it would require RIM to give another OS/device access to their network. And frankly, BBM is about the only thing they've got going for them. To me, the fact that they have a commercial solely focused on their Instant Messaging app reveals exactly how little they have to offer compared to iOS, Android, WinMo, and Symbian.