What Are Unlocked Cell Phones?

Unlocked cell phones, also known as GSM unlocked phones, SIM unlocked phones, or TDMA unlocked phones work with GSM carriers around the world. Unlocked phones can be used in the US with T-Mobile, Cingular and other GSM Carriers.

There are two types of unlocked phones: Original Equipment Manufacturer phones and Carrier/ Operator unlocked phones. Phones included in the first category have never been assigned to any carrier. Major OEM unlocked phone manufacturer's are Nokia, Motorola, Sony Ericsson, LG, Siemen and Samsung. Operator unlocked phones were initially "locked" to work with SIMs issued by a specific company and feature carrier logos and customization.