While iPhone 4S pre-orders in the US seem to be working just fine, international demand for the 4S has caused Apple to push back the shipping estimate for the 4S to 1-2 weeks. Instead of the assured delivery date on October 14th that Apple originally promised, shipping estimates for the 4S have slipped to a more uncertain delivery date for international customers.

Apple stores in countries like Canada, the UK, France, Germany, and Australia have all had shipping dates pushed back already. The iPhone 4S became available for pre-order after 12AM this morning…

The 4S was supposed to be available for pre-order at 12:01AM PST on Friday, but Apple’s online store and carrier pre-order pages took nearly an hour to become fully operational. Like most iPhone pre-order launches, huge amounts of traffic began to hit Apple’s website at once throughout the night. Traffic bottlenecks on both Apple.com and carrier websites blocked many customers from completing their pre-orders.

Within 4 hours of the pre-order floodgates opening internationally, shipping estimates for the 4S got pushed back to 1-2 weeks.

MacRumors reports:

“Apple eventually shut down its iPhone pre-order system for a brief period of time, bringing it back up to issue reservations that would allow users to return later to verify eligibility and select their service plans. Apple has begun notifying users who placed early reservations that they may now return to apple.com to complete their orders, and that they must complete the process by 5:00 PM Pacific Time tomorrow in order maintain their priority order status.”

Customers that wish to buy an unlocked GSM iPhone 4S have to wait until November.

Have you had trouble pre-order an iPhone 4S in one of Apple’s international stores? Let us know what the experience was like for you in the comments below.