Datasheet

11
Chapter 1: Beginning at the Beginning
Figure 1-2: How many bars do
you have?
The nitty-gritty of how your phone works
As soon as you turn on your phone, several
things happen. As the phone is powering up, it
begins transmitting information to and receiv-
ing information from nearby cellular towers.
The first information exchanged includes your
phone’s electronic serial number. Every cell-
phone has its own unique serial number built in
to the hardware of the phone; the serial number
in current-generation cellphones can’t be dupli-
cated or used by any other phone.
The technical name of this electronic serial
number depends on your cellular carrier.
AT&T, T-Mobile, and U.S. Cellular call it an
International Mobile Equipment Identity (IMEI)
number. Verizon and Sprint refer to it as an
electronic serial number (ESN).
It doesn’t matter to the phone or the cellular
tower if you’re near your home when you turn
on your phone — that’s the joy of cellphones.
All the cellular networks have agreements that
allow you to use cellular networks in other
parts of the country and, sometimes, around
the world.
That said, a call outside your cellular provider’s
own network may be expensive. Within the
United States, many service plans allow you to
pay the same rate if you use your phone any-
where in the United States to call anywhere in
the United States. But if you travel outside the
United States, even to Canada, you may end up
paying through the nose. Remember: Before
you leave on a trip, check with your cellular car-
rier about your rates. Even if you travel interna-
tionally only a few times every year, a different
service plan may work better for you. Your cel-
lular carrier can fill you in on your options. For
more on billing, check out the section “You and
Your Shadow: Understanding How Your Cellular
Carrier Bills You” in this chapter.
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