IMO, when I worked in admissions I really really preferred email and I think the students that contacted me by email got the best answers. With an email you can take the time to really look into their file and their situation and give a well-thought-out answer when you have the time to do that. When a student phones you have to deal with understanding what they want (often people are nervous on the phone and mix their questions up), people knocking on your door or coming into your office while you're talking, trying to look up the students details in the database etc. all at once. It stressed me out.