TELECOM Digest OnLine - Sorted: Re: Do Cell Phones Still Offer "A" and "B" Carriers?

Re: Do Cell Phones Still Offer "A" and "B" Carriers?

Isaiah Beard (
Mon, 16 May 2005 16:27:52 -0400

John Levine wrote:

>> Do today's cell phones have any option to do that?

> None that I've seen. Typically the A carrier is TDMA or GSM, and the
> B carrier is CDMA,

Not always true. I know of markets in Texas and New Mexico where the A
and B carriers are both CDMA.

Nonetheless, carriers nowadays have "preferred roaming agreements"
with various carriers in different regions, and often prefer that if
you roam, you roam on those carriers. In the case of CDMA, switching
to the right band is governed by a "preferred roaming list" (PRL) that
is loaded into the phone's firmware. If the phone can't find its home
SID, it will scan for other available SIDS based on a "priority list"
and lock onto the first one it finds. This ensures that the carrier
gets the "cheapest rate" for roaming. GSM has something similar (I
forget the name of it), as does Nextel (called a "band map").

Of course, this takes the ability to chose a roaming carrier out of
the hands of the end user, but for that sacrifice, you get expanded
coverage at "home" rates. None of the large wireless carriers cover
every inch of the nationwide network they advertise. A lot of holes
are filled by these preferred roaming partners who agree to charge the
carrier a discounted rate, who then in turn bills you as if you were
on the "home" network. In exchange, the roaming partners are
guaranteed a revenue stream from all users of the large wireless
carrier that pass through their territory. That's where the PRL comes
in (and why end users lost tha ability of manual control).

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