2. Use A Professional Voice Actor (from Fiverr) If your answering system lets you supply your own mp3 or wav audio files for the greetings, consider hiring a pro to record it for you.
Consider for a moment how your phone is currently being answered. Professional courtesy is quite often not the standard for many college students. An abrupt "Yeah!" could be listed among the more courteous greetings. The more outrageous remarks will often buy you a major black mark in the professionalism category—even if it was your roommate answering your phone and acting crazy. A simple "This is ____" is always a pleasant change for a college student call. Make the change today, before the next (or first) employer phone call. If you have a landline, you should also encourage your roommate to do the same.

3. Be mindful of your voicemail message. You need to confirm they've reached the right place, that the message will be confidential (make sure it is) and what you want them to do next.
My wife and I can’t come to the phone right now, but if you’ll leave your name and number we’ll get back to you as soon as we’re finished.