A note that many foreign pilots may not be aware of:
On 3 Aug 2013, all -121 (Delta, Alaska, American Eagle, SkyWest, Miami Air, Pace, etc. etc.) airline pilots will need an ATP to fly the plane.
Specifically, ALL pilots, both the Captain and the First Officer will need full U.S. ATP licenses to fly any -121 airplane. This law had about a 5 year time delay, so there is no grandfathering. If you are a -121 First Officer, without an ATP, you will not be flying after 2 Aug 2013, for your airline, anymore.
Also, the U.S. does not have a PIC ATP and an SIC ATP, like most of the rest of the world does. The U.S. also does not have a "Frozen ATPL". You will need the full ATP, that currently requires a minimum of 1500 hours total time, plus a bunch of other requirements, before you can set foot in the right seat of any -121 U.S. airline.
Currently the -121 First Officer can fly with just a Commercial License and an Instrument Rating. Only the Captain currently requires the ATP.