Today AT&T made a statement saying they would allow "seamless transition from their 3G network to any one of their 20,000 Wifi wireless hotspots". While the IEEE protocol wasn’t stated, it is likely the way that the iPhones will switch back and forth between 3G and Wifi.
There is always the possibility that they are doing "dumb handoffs" as well which would just be like when a normal iPhone enters an area which a recognized network is present. The iPhone finds the network, knows the password and switches over.
802.21 is an IEEE emerging standard. The standard supports algorithms enabling seamless handover between networks of the same type as well as handover between different network types also called Media independent handover (MIH) or vertical handover. The standard provides information to allow handing over to and from cellular, GSM, GPRS, WiFi, Bluetooth, 802.11 and 802.16 networks through different handover mechanisms.
AT&T’s press release:
AT&T* today announced it will support auto-authentication for iPhone OS 3.0 users connecting to AT&T Wi-Fi Hot Spots. Auto-authentication allows iPhone users to seamlessly switch from AT&T’s 3G network to an AT&T Wi-Fi Hot Spot without being prompted.
AT&T customers with qualifying iPhone data plans have unlimited access to the nation’s largest Wi-Fi network — more than 20,000 U.S. AT&T Wi-Fi Hot Spots.
The new process eliminates the previous two-step authentication, making it easier and faster for iPhone customers to connect to AT&T Wi-Fi. Auto-connect is established once a customer connects their iPhone to an AT&T Wi-Fi Hot Spot the first time.
The addition of auto-authentication for iPhone users comes at a time when Wi-Fi usage continues to experience rapid growth, driven by the proliferation of Wi-Fi enabled devices. More than 4 million connections were made at AT&T’s U.S. Hot Spots with smartphones, including the iPhone 3G, in the first quarter of 2009 alone.
AT&T is a leading provider of Wi-Fi enabled smartphones, and includes Wi-Fi access at no extra charge with qualifying AT&T High Speed Internet plans, 3G LaptopConnect plans and select smartphone plans.
“Auto-authentication makes it even easier for iPhone customers to stay connected on the nation’s fastest 3G network and the nation’s largest Wi-Fi network,” said Ralph de la Vega, president and CEO, AT&T Mobility and Consumer Markets. “With access to our U.S. hotspots, customers are receiving a great value, with a fast, reliable broadband connection virtually anywhere, through 3G or Wi-Fi.”
The new auto-authentication process is available starting today to all existing iPhone and iPhone 3G customers who download the free iPhone OS 3.0 software update via iTunes. It will also be available to all iPhone 3G S customers once that product goes on sale on June 19. Meanwhile, all iPhone customers can continue to get AT&T Wi-Fi access with the current authentication process.
AT&T’s Wi-Fi network complements its wired broadband and wireless 3G networks with Wi-Fi hotspots including retail stores, restaurants and airports from coast-to-coast.