To those of you who may rely upon AT&T to deliver your email-to-SMS messages for monitoring: some of you may be currently out of luck. I would just send this to the "outages@puck.nether.net" list, but it does seem to be a meta-network failure in that for better or worse many of us use SMS as a method to monitor outages, so this perhaps moves it up a notch in the importance hierarchy enough to warrant a NANOG post.
I am experiencing failures on my email transmissions to my older "blue" (aka: Cingular) AT&T devices at the moment, for both incoming and outgoing. Many of you may be using older "blue" cards in your NOC phones, SMS gateway devices, or perhaps even your personal mobile devices for those of you who still live in the dark ages of phones that aren't [2.5,3,4,x]G capable.
I am unable to diagnose the problems fully, but at least some (if not all) of the SMS-to-email gateway failures are due to mmode.com's MX hosts (in the "airdata.com" zone) being unreachable due to absence of functioning authoritative resolvers for that zone, and possibly other failures as well. This appears to be causing "550 Access Denied" messages being returned to my mobile devices that are sending to email addresses, and mail spooling on my Internet SMTP hosts that are trying to send to the "NPAxxxyyyy@mmode.com" addresses for SMTP-to-SMS relay.
There is a rumor that this is NOT related to the deactivation of the "downloads" components of the blue network on the 15th, but I suspect that someone just decided to pull the plug on everything. Reading to the end of the thread below, there is someone who states AT&T claims it will be back online by the evening of the 17th at the surprisingly accurate time of 9:55 PM (timezone unstated.)
More speculation:
http://forums.wireless.att.com/t5/mMode/URGENT-mmode-down-again-Their-mta01-cdpd-airdata-com-mail-server/td-p/1939480
I don't know if this is causing problems with anyone using TAP interfaces, or with any of AT&T's other SMTP<->SMS gateway services like @txt.att.net. SMS, and mobile devices in general, are a single point of failure for contacting on-call staff for various problems - perhaps it's time to insist that everyone carries two mobile devices, on different frequency and technology platforms, with different carriers, and split messages to both due to the anecdotally increasing failure rates of mobile networks. Conspiracy theories of how collusive unreliability would increase ARPU across the board for all carriers would be interesting to hear... but not in this forum, I suspect. 
JT