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.
An excellent business voicemail greeting conveys your level of professionalism and competence while also providing your callers with a glimpse into your company’s culture and level of care. As minor as it may seem, your voicemail greeting can instill confidence and trust in your callers or it can be a cause for concern.

A word of warning: These greetings will not do you any favors if you're in the midst of a job hunt or work in a conservative industry. Always remember your target personas. If there's a chance they won't appreciate your sense of humor, opt for a straightforward greeting instead.
At least if people who aren't the NHS or local gov't leave me voicemail, I will at this point have 0 compunction about just ignoring it because I did give them fair warning ;) Which in turn means I'm likely to call them back sooner...