We haven't verified exactly what's going on here, but we've gotten several tips tonight from people who've received an iPhone 4 pre-order cancellation email from Apple saying that their order couldn't be authorized. That sounds like an AT&T authorization problem to us, and given the litany of problems that Apple and AT&T had all week dealing with the huge number of pre-orders, we can't say we're too surprised to hear that the chaos continues. Here's the email:
Dear Customer,

We were unable to complete the authorization process for your iPhone order. As a result, we had to cancel your iPhone order. To complete the purchase of your iPhone, please visit an Apple Retail Store or an AT&T company-owned retail store.

We apologize for this inconvenience.

Sincerely,
Apple Online Store Team
Uh, yeah. We're obviously looking into the situation, and we'll let you know what we find out.

Update: We're hearing that some people are getting cancellations from AT&T, as well -- curiouser and curiouser.

[Thanks to everyone who sent this in]