In addition to the functional changes like AirPlay and AirPrint that we already know about in iOS 4.2, there are also under-the-skin changes that impact the way iPhones interact with cellular networks. The results of tests run at Nokia Siemens' Smart Lab in Espoo, Finland indicate that Apple has implemented a new control strategy that complies with the 3rd Generation Partnership Project's (3GPP) Release 8 specifications. The new fast dormancy feature in iOS 4.2 is said to significantly reduce signaling traffic between phones and the networks they operate on.
The way previous iPhones communicated with networks has been a topic of discussion for some time. Specifically, it was claimed that the way Apple's phone is controlled causes a lot more network traffic than other phones. Smartphone designers used an earlier version of fast dormancy that frequently shut down and restarted data connections to the network in order to preserve battery life. However, each time the connection changed state, signals were exchanged between the phone and network. The new protocol is controlled by the network rather than the phone, allowing operators to manage network traffic by slowing down the switching rate when things get busy. It's not known what impact this will have on phone battery life, but given that the phones were designed to optimize it with the old approach, it will probably be a bit worse when operating on busy networks. The change only applies to the iPhone 4, but any relief will probably be welcome on our increasingly crowded cell networks.