Let’s say you spent your vacation abroad a couple of years ago. Being thrifty, you removed your U.S. SIM card from your unlocked iPhone 4 and inserted a SIM card from a carrier in the country you were ...

If you’re thinking of moving to a new network, and want to keep hold of the same iPhone, you may hit a snag: the device is locked to your current carrier and can’t be used with any other company.

Sareena was a senior editor for CNET covering the mobile beat, including device reviews. She is a seasoned multimedia journalist with more than a decade's worth of experience producing stories for ...