SAN FRANCISCO  For many people on Friday, the iPhone was the iCan’t.

Apple suffered extensive network gridlock Friday morning, as many of the six million users of the original iPhone tried to upgrade to new software while the first buyers of the new iPhone 3G were trying to activate their purchases.

The setback was a classic example of the problems that can follow when complex systems have single points of failure. In this case, the company appeared to almost invite the problems by having both existing and new iPhone owners try to get through to its systems at the same time.

“There are certainly lessons in preparedness,” said Richard Doherty, a consumer electronics industry consultant who is president of the Envisioneering Group in Seaford, N.Y. He compared the day with Christmas morning, “the acid test for many years” for electronics companies because customers contact them in droves after opening presents and trying to get gadgets to work.