jargon that can save you money or broaden your possible destinations!
Most GSM phones purchased from a carrier store (such as Voicestream or
AT&T Wireless) come "locked" to that network, which means
that you can't use another Sim in your phone.
It also means that you can only go to the countries that have roaming
agreements with those particular carriers.
The Sim (subscriber identification module) is what holds your
information - your phone number, your billing address, etc. It is the
small white plastic chip in the back of the phone.
An unlocked phone gives you the ability to use different services when
traveling that might offer a broader range of coverage. For
instance, AT&T's GSM SIMS and service currently do not work in
Cambodia. But ours do. So you might need to use a different
Sim when traveling to some destinations.
Buying an unlocked phone typically adds to its price because of the
flexibility and savings that can be realized.
To see if your phone is locked, put a Sim from another carrier in the
phone. In other words, if you have a Voicestream phone, try to put your
friend's AT&T Wireless Sim in the phone. If you can make a call, it
is unlocked. If the screen reads "enter correct Sim" or
"Sim unrecognized," the phone is locked.