Toyota is currently running a national print ad promoting the company’s future eco-friendly technologies. As you would expect, it pictures a Toyota Prius glistening by a tree-lined lake, and brags about the fuel and CO2 saved by hybrid technology. The ad copy says that Toyota’s current hybrids are “paving the way for the next generation of environmental vehicles.” And then these five words: “Like cars charged at home.”

Sounds innocent enough, but those five words signal a big shift for Toyota as it finally moves forward with plans for a plug-in hybrid. Unlike Bob Dylan’s fans who sobbed and booed when he went electric at the Newport Folk Festival in 1965, Toyota’s hybrid followers are cheering the company’s intention to plug in, which could boost mileage on a Prius from 50 miles per gallon to the equivalent of 75 or so.

Starting in January, the company will put the first 500 official Plug-in Priuses on American, European and Japanese roads. The US will get 150 of the test vehicles, which use lithium ion batteries, not the nickel metal hydride packs that Toyota says are the current and long-term solution for conventional hybrids.

The pilot effort will kick off a three-year effort to get data on how plug-in cars fare in the real world: how they're charged, how their batteries perform, and what sort of mileage they get. "The target is 2012 to be coming to market with them," Irv Miller, group vice president for Toyota US Sales, said at a Los Angeles conference on climate change. Before that, "we're going to study the challenges of consumer demand," he said.