Wieselgren reported that the lab found that all these iPhones to “have no problems with the 3G communication in the test chamber. They send and receive signals in a fully normal manner. They do not disconnect earlier than the others we have tested when the signal becomes weaker.”

“The power control issue will also have an effect on the data throughput, because the higher the data rate the more power the Node B transmitter requires to transmit. If the UEs have poor power control and are taking more power than is necessary then it will sap the network’s ability to deliver high speed data.”

“This is one of the reasons why AT&T has been sending text messages to users to persuade them to upgrade to the 2.0.2 software. In a mixed environment where users are running 2.0, 2.0.1, and 2.0.2, the power control problems of 2.0 and 2.0.1 will affect the 2.0.2 users.”

“It is not the network that is fault but the interaction of the bad power control algorithm in 2.0 and 2.0.1 software and the network that is at fault. The sooner everybody is running 2.0.2 software the better things will be. Having seen the graphs the 2.0.2 software has already started to make difference.”

That explains why some users saw no immediate impact after installing iPhone 2.0.2, and why tests of individual iPhone 3G models showed no significant difference between the 2.0 and 2.0.2 software: the problem was only evident when a critical mass of phones all acted in concert to run a given cell tower out of power. This also explains why users in locations such as San Francisco and New York were seeing bigger problems than users in less densely populated areas where fewer iPhone 3Gs were in use.