UPDATE: Some users have had success using the Apple Store iPhone app to reserve the iPhone 4 for pickup.
A number of users are experiencing difficulty pre-ordering the iPhone 4, as Apple and AT&T servers appear to be crushed by demand for the new device.
Users attempting to pre-order from the online Apple Store are receiving one of two error messages:
Users attempting to pre-order from the AT&T website are receiving the error message:
Some users have who have gotten to the point directly prior to checkout but can proceed no further have found that adding another item to the cart allows them to successfully move to the checkout screen. The item can then be removed and the iPhone 4 pre-order placed.