TextPlus is another free texting app. If you use it to text a cell phone, it counts just like any other text for the person who gets it. There is no charge to you to use the Text Plus program. I have an iPhone, but no text plan because I just use TextPlus to send and receive texts for free (it uses data from my plan if I'm using the 3G network instead of wi-fi, but no per-text fees.)
If you are communicating with another i-device (ipod touch 4th gen, iphone), you can use their messenging thing as well.
messages using a 4th gen touch. She can only spell six words (mom, dad, her name, I, love and you). When she wanted to send a longer message, I wrote it down for her and she copied it word by word and the message. I figure it is good literacy practice. She My four and a half year old has been having a ball sending us text reads the messages we send back to her too.