This is sort of interesting. I got a 3G data modem back at the end of last year. These devices have phone numbers, though they can't make or receive traditional voice calls. They can, however, send and receive SMS messages. I don't have any use for this, so I've ignored it, but last month a text message from the Philippines, of all places, showed up. I called up AT&T and they took it off the bill (it was 42¢ for one text!) and opted-out of SMS. And that was the end of it.
Last night, just as an experiment, I loaded up the Novatel Mobilink software to use the modem in the USB mode on a Windows XP virtual machine, just to see how it would work. And after some fiddling, I did get it working.
The interesting part is that in the Mobilink UI, there was a little mailbox icon. Clicking on that took me to an SMS management UI, which showed not one but 5 text messages waiting. The other four were free texts from AT&T warning me that in January and April I was approaching, and then exceeded the usage limit of my plan (back then I was on the 200 MB/mo plan).
The interesting part is that I didn't have the MiFi back then. That means that incoming SMS messages must either be stored in the network somewhere or on the SIM.
It's sort of too bad that the MiFi can't share the unlimited text messaging we have on our two iPhones. Alas, to properly make use of it, Novatel would need to add SMS support either into the MiFi SDK (so that you could write an app or a widget to use it), or - better yet - into the MiFi's web UI (preferably behind the admin password somewhere).