NOTE: There are quite a few “catches” to this free service so if you plan on using this app to save a little bit of cash I recommend reading it all!
Tashanna pointed out a thread to me on PinStack mentioning a free texting application from Mjoy. The application is a small java application that worked on my Bold but I cannot promise that it will work on yours. It will let you send a text message to quite a few countries for free. I would just recommend that you tell the person not to reply since replies will be sent back through the carriers SMS system.
Once again I have to stress that this is NOT a application developed specifically for BlackBerry and I only used it for a short while so no promises that it works for you. The app does append a message of "Text for FREE with http://mjoy.com" at the end of your message so keep that in mind. The receiver might also have to pay for receiving the message… If you both have the application installed it is free to send messages between the two of you as long as you have unlimited data otherwise data costs will be incurred.
Kudos to Seabirdone for the find!