I had three phone interviews with Amazon that spanned from late September to late October. The questions were not hard but like other postings have already said doing it over the phone made it somewhat difficult. I was never asked any conceptual questions in any of the interviews rather each interview was one or two problems to be solved. Overall every interview I had was pleasant the interviewer would drop hints to lead you in the right direction or ask if this was the best solution. From the delay after the third interview I figured the interview process was not going to go further but three weeks seemed like a while to send out a rejection letter. There was a good week or two between each phone interview so it would seem Amazon was doing a lot of interviewing during this period.