 Although the concept of home audio entertainment was attractive to potential U.S. subscribers, the lack of signal amplification and other technical limitations, such as the need to maintain a telephone line infrastructure, and having to listen over headphones, made the technology unprofitable.Less than a decade after the failure of the Telephone Herald companies, radio broadcasting was developed, which had the significant advantage that it could dispense with the need to use telephone lines.Moreover, radio programming could be provided free of subscription fees, because selling airtime to advertisers, the financing method most commonly adopted in the United States, provided sufficient revenue for ongoing operations.