Every phone call I've made to DL or NW in the last twelve months has been answered in a foreign country by someone with very basic English skills who was not very helpful. Check out the DL and NW FT forums and you'll see a lot of complaints about their call centers. And I'm a very patient person who works with non-US citizens on a regular basis, and am used to hearing English spoken with a thick accent. But some of the phone agents I've had with DL have been almost impossible to communicate with, and have not had much knowledge of anything other than the basics of booking a simple roundtrip ticket between two points.