Amex Fraud Alert
My guess is that Amex (and others) can't handle the volume of charges from a single vendor (Verizon in my case). I bought a MacBook Pro for around $2k direct from Apple in August, several other $1k+ charges in August and September (my balance is now $8k), so the $462.68 charge from Verizon isn't any big deal. I received both a phone call and an email from Amex today - had to deal with calling them to OK the charge, and then figuring out how to call Verizon (thanks to this thread for the phone#) to tell them to re-charge...
A couple of hours later there's another two emails notifying me of "Card Not Present" transactions of $462.00 to "CELLCO PARTNERSHIP" i.e. Verizon.
We'll see how many go through and finally end up on my Amex account.