Textfree app will let you send texts without owning a phone.

The business of text messages is a big one for wireless carriers and people seem not to mind using them a lot. Some of them even text more than they talk, specially teens and pre-teens. But for parents not ready yet to let their youngest own a cellphone or people whose ability to text is limited by their wireless' plan, there is a way to get around that. The solution is the possibility to send and receive text messages without a cellphone being involved. The only requirement is an iPod Touch and the willingness to download an app called Textfree from a company called Pinger. The service assigns users a real phone number and allows them to send and receive text messages for free. Users are connected through Wi-Fi with the only trade-off being the presence of banner ads at the bottom of the app.
With the assignment of a phone number, Textfree has the capability to offer also voice service.
That option is in the works with a beta phase set to debut in late September. Called "Textfree with Voice", the service will give users the option to pay for voice minutes or earn free minutes by performing tasks like downloading free apps, filling out surveys or performing other tasks, according to CNET.

For more, see CNET.com