Yeah, I think it is a software problem as well (hopefully!)
Sarge did a good explanation of the problem for the S here:
I get a similar type of graph, too, though I've never seen it go so low. Presumably it does, and that's when it kicks out the 'Emergency Calls Only' error.
So far I've only seen the issue crop up in three locations.
1: At work, on my desk, where I know the phone sometimes switches between T-Mob and T-Mob Orange. I suspect it happened here when it was switching carriers and had a fit. I had to restart the phone to get it back.
2: Sat on our sofa at home. My side of the sof has notoriously bad signal. It's pretty much bang centre of the house, and my iPhone 4 on O2 could never hold a signal there. The 4S was better due to the improved antenna. The One X, on T-Mob seems to keep dropping into 'Emergency Calls Only' mode here too, though it instantly reconnects. I only know it's happening because I have an app monitoring for it in the background.
3: Driving around our village. Again, I suspect this is happening when the phone is either switching towers, or switching between Orange and T-Mob. I know our area is one where this happens a lot because the wife sees Orange a lot on her T-Mobile iPhone 4S.
So, what I'm thinking is this - the issue I had at work was a bug that's related to the 'Emergency Call' thing but not quite the same due to the fact it needed a reboot. The issue of the logging app seeing disconnects seems to be related to the phone switching either carrier, masts or 3G/2G. Either way, it doesn't appear to be handling a handover particularly well and taking long enough for the phone to think something's wrong.
Does any of this fit with anyone else's symptoms? What about the stories in the One S forum?
I'm running the MaXimus 2.1 ROM which is the latest 4.0.4 version of Android with Sense and updated radio drivers. What about everyone else?
Long story short - I don't think it's hardware or it wouldn't reconnect so quickly, and if it was just poor at picking up signals then I'd have an iPhone 4-like experience with the One X on my sofa.
There, epic over