The Apple iPhone 4S went on sale at 8AM Friday morning in markets around the globe. In the U.S., people lined up by the thousands hoping to get the iPhone 4S on opening day. Crowds were largest at Apple's retail stores, though lines have been spotted at AT&T, Sprint, and Verizon Wireless stores as well.

Once the phone is purchased, owners need to activate it through iTunes. As has happened in years past, it looks like AT&T's servers aren't quite up to the task of handling thousand and thousands of new iPhone 4S activations all at once.

A quick Twitter search shows hundreds of complaints from iPhone 4S owners who are unable to successfully activate their new handsets on AT&T's network. While the phone can still be used (for watching movies, or listening to music) when not activated, the activation is necessary to make and receive phone calls, as well as to send text messages. Activating the phone is what ties that particular device to a user's account.

But wait, AT&T is not alone, not at all. In fact, Sprint iPhone 4S customers are reporting trouble activating their handsets, as well. According to a Twitter search for Sprint activations, plenty of users have been unable to activate their handsets and get them up and running on Sprint.

[ Are IT leaders losing the RIM religion? See RIM And Apple: Mobile Agony And Ecstasy. ]

Same goes for Verizon Wireless. Reports are surfacing on Twitter that Verizon's activation servers are running slow and/or have crashed. However, the number of people complaining about Verizon-related activation issues is far less than those reporting issues with AT&T and Sprint.

It was suggested to me by someone with knowledge of the situation that Apple's servers are most likely to blame for the problems. An employee at one of the three major carriers who asked not to be named told me in an email, "Yes, my IT people aren't happy. The activation issue is out of the Apple stores ... on all carriers."

Sprint followed up to say that the problems are not theirs, either. Spokesperson Michelle Leff said, "Sprint currently has no systems issues and no internal process issues that should impede device activations."

Whichever party's servers are responsible (cough, Apple?, cough), the activation issues speak to the sheer volume of people out buying new Apple smartphones today. Analysts have predicted that Apple may sell as many as four million iPhone 4S units during the opening weekend. Considering that more than one million fans pre-ordered the device for delivery today, and it sold out of first-day inventory at AT&T.com, Sprint.com, and VerizonWireless.com, Apple could have a very big weekend, indeed.

The iPhone 4S has a dual-core 1-GHz A5 processor; 8 megapixel camera with autofocus, flash, and 1080p HD video capture; HSPA+/CDMA, Wi-Fi, GPS, and Bluetooth 4.0 radios; Siri personal assistant, and iOS 5. It maintains the same size, shape, design, and appearance of the iPhone 4.

The 16-GB model costs $199, the 32-GB model costs $299, and the 64-GB model costs $399.