Google Voice for Mobile Phone
Get extra calling power by integrating Google Voice into your phone. Once you've signed up for an account, download the official app and watch your options expand. Bonus tip: Add the Google Voice widget to your home screen for one-touch toggling of your outgoing-call preferences.
You can send text messages for free through Google Voice--everything you need is in the app. Just make sure you change the settings to refresh every 5 minutes so that incoming messages won't be delayed. If you want faster notifications, log in to the Google Voice Website and configure your account to send you e-mail alerts when a new text arrives.
Note: This link takes you to the vendor's site, where you can download the latest version of the software directly onto your phone.