WhatsApp has been available for the iPhone for quite some time, but it is just now making its way to BlackBerry as well. The app is still in the (very) early stages, so the UI and features leave a bit to be desired, but WhatsApp is delivering free smarthphone-to-smartphone messaging. What this means is that you will be able to send messages to all of your iPhone toting buddies for free. WhatsApp uses the phone numbers in your address book and works over your data plan, so you won't incur any additional SMS charges. You can send "a million messages a day" and it won't cost you a thing (aside from the $2.99 purchase price). The app definitely has a way to go in terms of design and function, but its a good start. If you have a few friends who refuse to convert to BlackBerry, you may want to give WhatsApp a go. While the price may be a bit high for some ($2.99 in App World vs. $0.99 in iTunes) it may be worth it if you're a message hound. Check out WhatsApp in BlackBerry App World for more.