VoodooVox provides detailed demographic information on phone numbers. They source this information by mapping the number against numerous 3rd party databases typically used by the direct mail industry.
This data feed is available to developers via an API. Developers pass in phone numbers, and demographic info is returned. Users have access to city, state, zip code, and cell carrier for any phone number queried through the API with 200 fields available. Caller Analytics submits call records in real-time through the API giving users an analytics portal for their call activity. The API uses RESTful calls and responses are formatted in JSON.