You need an iPhone as well as the iPad for the text messages to work on your iPad.... As long as your iPhone and iPad are online, as soon as your iPhone receives an SMS or MMS message, it will relay it through Apple's messaging servers to your iPad. And, whenever you want to contact a "green bubble friend" from your iPad, Apple's messaging servers will relay that to your iPhone, and from there, out over the carrier network. It means, if you're on your iPad, and you need to text, you'll never have to go chasing after your iPhone again...