mysms is a great app/webservice that uses cloud storage to let you text from Android, iOS (iPhone, iPad), Windows, Mac OS, and even through the website. I opted for the Chrome extension that is really just a bookmark with a nice button, but all versions provide a unified experience. Install one copy on your phone, and log in from any other and you’re in business texting from your new iPad or from a browser on a borrowed computer. The only catch is that your phone needs to be on, and connected to the Internet. For someone worried about carrying their brand new iPhone 4S to school, but who wants to get that important SMS, this is the service.
Free, as are most of the services I use: mysms