Sunday March 30 is the start of Open Skies, a set of new rules that allows U.S. and EU airlines to operate transatlantic flights between any cities they like.

Virgin Atlantic, for instance, could operate Paris-New York or Rome-Atlanta flights--without originating the flights from Britain.*

The largest, immediate change is at Heathrow airport. More than 100 new flights per week between the U.S. and Heathrow will take off, starting next week.

Until now, only four airlines could offer service to the U.S. from London's Heathrow Airport: British Airways, Virgin Atlantic, United, and American. But later this year, Continental, Delta, Northwest, and US Airways will begin flying into Heathrow—which is closer to central London than Gatwick, the airport most Americans arrive at now.

Prices may or may not drop.

The following airlines plan to add nonstops to Heathrow this year:

Detroit, Minneapolis, and Seattle (Northwest)
Philadelphia (US Airways)
Newark and Houston (Continental)
L.A. (Air France-KLM)

In related news: American plans to switch all of its Dallas and Raleigh, N.C., flights to Britain from Gatwick to Heathrow, according to the AP.

*CORRECTION: This blog post originally cited SAS Scandinavian Airlines's announcement of a Copenhagen to San Francisco nonstop flight as an example of Open Skies. That was incorrect, and the Virgin Atlantic example has been substituted. Thanks, Bo, for the correction.

Adding confusion, British Airways is launching an airline in June called OpenSkies, flying from Brussels and Paris to New York City without stopping in Britain.

EARLIER JetBlue begins to offer more legroom for a fee.