iPhone Dev team has posted a video that shows you could send SMS messages from iPad 3G. They are still working on this tool that will require you to jailbreak iPad to send SMS messages. There is still no GUI for this tool; however the video shows an SMS being successfully sent from iPad 3G using command line terminal interface. Here is the video:

Spirit Jailbreak for iPad is now available that can be used to jailbreak iPad 3G. So, now all you need is to wait for the tool to arrive. As you’d be aware, there is no unlock for iPad available as yet so it won’t be possible to use any other sim than AT&T’s. Perhaps we can expect phone calls using jailbroken iPad soon too.

Source: RedmondPie