Typically the set up a phone interview via email.
Phone interview was done on a conference call with multiple people in the room listening in, including the office manager, senior engineer, and a few other people from the staff. Phone was very muffled and I found it very hard to understand them. This caused a lot of miscommunications and me asking "what?" a lot.
The questions were straight-forward. Asked about course work, interests in the field, and some feeler questions to get to know you better. No real curve-balls to speak of.
I would assume if you impressed them enough over the phone interview they would invite you out to visit their office. I knew after I hung up that the interview did not go well, so I wasn't expecting a call back.