There is actually a pretty good synopsis of limitations to E911 technology here, but I wish there were a link to the independent study mentioned. Their link to a Consumer Reports article on E911, however, is worth a read even if it is over two years old. It’s the first place I’ve heard of “lock-in”, or as they describe it, when your cell phone “is programmed to preferentially seek out the signal from the home carrier even if another carrier’s signal is stronger”. At the time the article was written, all-digital cell phones were not required to use a competitor’s network if the subscriber’s network did not get through to 911. That doesn’t mean they wouldn’t, but it’s certainly implied. I need to find out if this has changed in the last two years.
The Emergency Network Myths site itself is part of a larger site promoting the company, SATTEL, and their location-detection product SafeLink, which I need to research a little further.
Regardless, we’ve got a long way to go before cellular E911 is as effective as it needs to be.