The Open Skies Agreement that allows airlines to fly to the U.S. from any EU airport (not just their home country) went into effect this weekend and is predicted to stimulate slot trading and alliances between carriers ... perhaps even some mergers and acquisitions. The idea behind the agreement is to broaden competition among airlines. Under the old rules, just four airlines could operate flights to the U.S. from Heathrow. Now prime slots could potentially change hands for very high prices, or alliances may be formed. But even more change is expected should current regulations on European investment in American airlines soften.