There is a good discussion of this issue in the Troubleshooting Cisco IP Telephony book. The @ actually calls up the whole collection of patterns that are in the NANP, you can actually look at this whole thing in C:\Program Files\Cisco\DialPlan\NANP. You can use route filters to modify it, but you need to really study what all the tags do, etc. For very straightforward installs, it is probably fine, but many situations end up with complicating factors. We usually do as described above, with a set of patterns in different partitions for each location. The System Guide has some good info:
Using the @ Wildcard Character in Route Patterns
Using the @ wildcard character in a route pattern provides a single route pattern to match all NANP numbers, and requires additional consideration.
The number 92578912 matches both of the following route patterns: 9.@ and 9.XXXXXXX. Even though both these route patterns seem to equally match the address, the 9.@ route pattern actually provides the closest match. The @ wildcard character encompasses many different route patterns, and one of those route patterns is [2-9][02-9]XXXXX. Because the number 2578912 more closely matches [2-9][02-9]XXXXX than it does XXXXXXX, the 9.@ route pattern provides the closest match for routing.
When configuring route patterns, take the following considerations into account:
•When @ is used in a routing pattern, the system recognizes octothorpe (#) automatically as an end-of-dialing character for international calls. For routing patterns that do not use @, you must include the # in the routing pattern to be able to use the # character to signal the end of dialing.
•If the route pattern contains an at symbol (@), the Discard Digits field can specify any discard digits instructions (DDIs).
The "Special Characters and Settings" section lists DDIs and describes the effects of applying each DDI to a dialed number.
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_chapter09186a00803edabe.html#wp1050657
And the Admin Guide
Route Filter Tag Descriptions
The tag serves as the core component of a route filter. A tag applies a name to a subset of the dialed-digit string. For example, the NANP number 972-555-1234 comprises LOCAL-AREA-CODE (972), OFFICE-CODE (555), and SUBSCRIBER (1234) route filter tags.
Route filter tags require operators and can require additional values to decide which calls are filtered.
The values for route filter tag fields can contain the wildcard characters X, *, #, [, ], -, ^, and the numbers 0 through 9. (See Table 15-3 in the "Special Characters and Settings" section of the Cisco CallManager System Guide for definitions of wildcard characters.) The descriptions in Table 15-2 use the notations [2-9] and XXXX to represent actual digits. In this notation, [2-9] represents any single digit in the range 2 through 9, and X represents any single digit in the range 0 through 9. Therefore, the description "The three-digit area code in the form [2-9]XX" means that you can enter the actual digits 200 through 999, or all wildcards, or any mixture of actual digits and wildcards that results in a pattern with that range.
Route filter tags vary depending on the numbering plan that you choose from the Numbering Plan drop-down list box on the Route Filter Configuration window. Table 15-2 describes the route filter tags for the North American Numbering Plan.
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_chapter09186a00803ed67d.html#wp1032663
And even this old tech note
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_tech_note09186a0080094b2a.shtml
Mary Beth
