A method and system for number indexing for advertising. Alphanumeric identifiers (e.g., telephone number, voice-over-Internet Protocol identifier, an Internet Protocol identifier, an instant message identifier or an e-mail address identifier) are used to categorize and associate pre-determined advertising with the alphanumeric identifiers. When the alphanumeric identifier is received on a communications network, the pre-determined advertising associated with the alphanumeric identifier is sent to a target device.