Had a phone interview for summer internship. Was expecting casual chat with some technical questions, but the interviewer had a complete exam with multiple choice questions. The questions weren't simple enough to be done in the head, needed a pen and paper to write down the questions, draw figures, write and solve equations. I was surprised that phone interviews could be so technical, having had no prior experience of interviewing for jobs in the US. I did quite badly because I had not gone over most of the content in a long time. The questions were from these general areas: signal processing, probability and statistics, information theory and communication systems.