A US Phone custom field type will validate the Area Code and Central Office, or Exchange, Code to ensure it is a valid phone number.

Allowed Toll-Free Numbering Plan Area Codes

"800", "822", "833", "844", "855", "866", "877", "880", "881", "882", "883", "884", "885", "886", "887", "888", "889"

Allowed Restricted Numbering Plan Area Codes

"600", "622", "633", "644", "655", "677", "688", "456", "700", "500", "521", "522", "523", "524", "525", "526", "527", "528", "529", "532", "533", "535", "538", "542", "543", "544", "545", "546", "547", "549", "550", "552", "553", "554", "556", "566", "558", "569", "577", "578", "588", "589", "900", "710" 

Area Code Format

Allowed ranges: 2-9 for the first digit, and 0-9 for the second and third digits. When the second and third digits of an area code are the same, that code is called an easily recognizable code (ERC). ERCs designate special services; e.g., 888 for toll-free service. The NANP is not assigning area codes with 9 as the second digit

Exchange Code Format

Allowed ranges: 2-9 for the first digit, and 0-9 for both the second and third digits (however, in geographic area codes the third digit of the exchange cannot be 1 if the second digit is also 1).

Examples

Valid

8885551234 - The Area Code is a toll-free number.

18885551234 - 11 digits, starting with 1 is allowed when the number is toll-free.

Invalid

9324113325 - The Exchange Code (411) does not allow for the third digit to be 1 if the second digit is 1.

1234567890 - The Area Code (123) does not exist.