If you have a habit of chatting on-the-go, here's a news flash: Yakking for long periods with the set in direct contact with your face can lead to "acne mechanica" or pimples caused by friction. Because mobile phones are rarely sanitized and frequently placed on many surfaces or dropped in public places, they're exposed to lots of bacteria.
Spot-busting tip: Wipe your phone regularly with anti-bacteria wipes and try to hold the phone slightly away from your face while talking.