vText lets you receive and send SMS ,via an android mobile phone.
Install vText app on both iPad and android phone(OS 2.2 and later), login your Google account on iPad(needs to be the same account you use to login Android phone), allow push notification in iPad vText app, and youre all set.
When ever your android phone gets an SMS, your iPad will receive a push alert, you can read the message and reply directly within the app.
Since all SMS are transfered via your android phone, a 10-20 seconds delay per message is expected.