Happens a lot in LA
I live on the west side of LA and get this message fairly frequently. I find that the ATT Edge network is horrible... I love the iPhone, but the network is pretty bad.
I get the "could not activate Edge" message sometimes several times a day - I've called, and of course ATT has nothing useful to say about the issue. Browsing the web is a bit of a joke.. unless you're really, really patient.