Samsung SPH-M300ISASPR - Manual (Page 40)

16 Section 2A: Your Phone: The Basics
4. Power/Accessory Interface Connector allows you to
connect a power cable and optional accessories such as
a USB cable or a hands-free headset for convenient,
hands-free conversations.
5. Camera Key allows you to take pictures when in camera
mode.
6. Headset Jack allows you to plug in an optional headset
for convenient, hands-free conversations.