We send emails too, but it's also nice to get a TXT on your phone for really urgent information such as a problem with the server.
I think this approach is neat and novel, but ultimately I don't believe they've solved their problems.
YAPS/SMSClient with a good gateway SMS provider, if the SMS is that critical. I don't understand why email only is a failure, assuming they have push email to their phone (and if you don't, well why not?)
And this is coming from someone who has completely bought into the "OMGTWITTER" phenomenon. ;)