JaxtrSMS is aÂ free andÂ open mobile to mobile texting application.Â Jaxtr service allows you toÂ send messages/sms to all in your address book whether they have the app or not for FREE. It works on WiFi & 3G. You canÂ find more about the service at ttp://www.jaxtrsms.com/home.html. Its good to see more cross-platform services paying attention to Windows Phone platform.
Download the free app here from the marketplace.