Para hablar con una persona en American Airlines, sigue estos pasos:

the part of a country that borders another country; boundary; border. the land or territory that forms the furthest extent of a country’s settled or inhabited regions. Often frontiers. the limit of knowledge or the most advanced achievement in a particular field: the frontiers of physics.

Source: https://support.google.com/admanager/thread/306598761?hl=en&sjid=629569326575332752-AP