My last rant o the day...
We are in a congested tristate area. Firms and individuals may have phone numbers with multiple area codes. In company contacts, the area code is listed for the primary; I guess it is assumed that fax and cell numbers will have the same area code. I know of companies with an 800-xxxx-xxxx main number, a 703-xxx-xxxx fax number and individuals with 240-xxx-xxxx cell numbers, all valid and local.

For basic functionality, all phone numbers MUST show all 10 digits.