It seems like text messaging fills this gap for 90% of users. Yes it sounds a lot better to me, but aren't the mobile carriers going to hate (resist, etc) something that undercuts their cash cow of .25$ text messages?
It's been around for years now, and it's pretty much an accepted utility across the board. Remember, carriers get to charge extra for the Blackberry data plan.
To me, it's pretty much the same as the carriers not being too fond of, say, mobile AIM. They still get their data plan cash, though. The sooner more people/services move to BBM, the sooner I can get rid of my outrageously priced text messaging plan.