RIM released an update to its BBM software, BBM 7.0 has been released with a new good feature. Voice over WiFi networks, you can now chat with voice with your BBM contacts when both are connected to WiFi networks.
Both iOS and Android already had this option long time ago. Now Blackberry users can also talk for free with other Blackberry users while on WiFi network.
Blackberry still needs to improve a lot of other things to still be able to catch some of the smartphone users. But I think it is on the right way now.
With 3G tethering (OS 7) and Voice over WiFi with (BBM 7) it is going after iOS and Android.
BBM 7 is now available for download for OS 6 and above, but it will be available for OS 5 devices in a near future.