Proven possible already by Musclenerd last week, SMS support for the iPad was however still very limited. Fortunately, jailbreak app developers SwirlySpace gave it a spin as well and apparently managed to run their SwirlyMMS app on the iPad 3G.
It's not quite ready yet as they're still working on the interface (give it one or two weeks), but they claim to already be able at this time to both send and receive SMSs and MMSs natively. If true, that's quite an achievement. Check it out: