E-mail. The safest bet.
It's the future now. E-mails come to me quickly and stare me in the face until I action them. Easily the best way to get a hold of me, probably the easiest to remember too!
Phone. Still works.
Though, it spends most of it's time on silent. Be sure to leave a detailed message with your name, number, and availability. A text message would also be fine.