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.
Business professionals are also encouraged to keep their voicemail organized. Delete any messages from the office phone that are no longer necessary after calls are returned, and write down any phone numbers that are needed at the time the message is listened to. If modern voicemail service is utilized, such as that supplied by Voicemail Office, in which voicemail and fax messages are received in a staff member’s email inbox, the individual should write a short explanation in the body of the email if forwarding any voicemail messages to other staff members.

Leave out excuses like “I’m probably with a client right now” or “I’m unable to answer the phone right now” – it’s obvious you can’t answer your phone if a caller is listening to your voicemail greeting!
If you are on vacation/out of the office, be sure to record a special message to let people know when you left and when you are expected back.