AT&T loves WiFi. And it knows that you love WiFi too. So it just bought up WiFi hotspot operator Wayport for $275 million in cash. The acquisition will add about 3,000 WiFi hotspots to AT&T’s network in the U.S., bringing the total to 20,000 hotspots (including those in Starbucks and McDonald’s).

The company cites estimates that 300 million WiFi laptops, cell phones and other devices were shipped in 2007, growing to one billion by 2012. The growth is going to come from WiFi cell phones. Already, the iPhone, Blackberry, and Android phones, among others come with WiFi. That will soon be standard on most Internet-capable phone.

A bigger WiFi network helps AT&T’s wireless business because it provides a way to offload data-intensive traffic from its 3G cellular network to the cheaper and faster WiFi networks, where available. That is why AT&T offers free WiFI connections to all of its iPhone and Blackberry customers. Expect that trend to continue.