Nothing! you might end up interviewing your interviewer. Its a 5 minute call and they'll hire you regardless of how you did in the interview but they would ask following;
1) Do you have smartphone?
2) Do you have a data plan?
3) Are you comfortable standing for long periods of time?
If you answered all these questions in a "YES", Congratulations! you are hired!
Don't, you'll probably end up interviewing the interviewer
They will hire anyone - as long as you got a pulse