TextNow is a universal application that allows you to SMS/Text message for free from your iDevice. Once you have download the App, simply sign up for free(takes about 1 minutes), and the App will give you a number. This is a brand new number, not the number people normally call you on. But the great thing about this is that the number is 10 digits. That way there will be no confusion when contacting your friends or giving them a second number so they can text you. MMS is free as well, TextNow is a just a great App and could even get you to cancel your SMS plan.
Check it out in the App Store:
TextNow - Unlimited Free Texting and Picture Messaging (SMS & MMS) for iPhone, iPod touch, and iPad on the iTunes App Store