Page 167 - Asterisk™: The Future of Telephony

Pattern-matching examples
Before we go on, let’s look at a few more pattern-matching examples. In each one, see
if you can tell what the pattern would match before reading the explanation. We’ll start
with an easy one:
_NXXXXXX
This pattern would match any seven-digit number, as long as the first digit was two or
higher. This pattern would be compatible with any North American Numbering Plan
local seven-digit number. In areas with 10-digit dialing, that pattern would look like
this:
_NXXNXXXXXX
Note that neither of these two patterns would handle long distance calls. We’ll cover
those shortly.

The NANP and Toll Fraud

The North American Number Plan (NANP) is a shared telephone numbering scheme
used by 19 countries in North America and the Caribbean. Countries within NANP
share country code 1.
In the United States and Canada, telecom regulations are similar (and sensible) enough
that you can place a long-distance call to most numbers in country code 1 and expect
to pay a reasonable toll. What many people don’t realize, however, is that 19 countries,
many of which have very different telecom regulations, share the NANP. (More infor-
mation can be found at http://www.nanpa.com.)
One popular scam using the NANP tries to trick naive North Americans into calling
expensive per-minute toll numbers in a Caribbean country; the callers believe that since
they dialed 1-NPA-NXX-XXXX to reach the number, they’ll be paying their standard
national long-distance rate for the call. Since the country in question may have regu-
lations that allow for this form of extortion, the caller is ultimately held responsible for
the call charges.
The only way to prevent this sort of activity is to block calls to certain area codes (809,
for example) and remove the restrictions only on an as-needed basis.

Let’s try another:
_1NXXNXXXXXX
This one is slightly more difficult. This would match the number 1, followed by an area
code between 200 and 999, then any 7-digit number. In the NANP calling area, you
would use this pattern to match any long-distance number. ‡
Now for an even trickier example:

_011.

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