State and local agencies that provide emergency telephone services must provide "direct access" to individuals who rely on a teletypewriter (TTY, also known as a telecommunication device for deaf persons or TDD) or computer modem for telephone communication. Telephone access through a third party or through a relay service does not satisfy the requirement for direct access. Where a public entity provides 911 telephone service, it may not substitute a separate seven-digit telephone line as the sole means of access to 911 services by nonvoice users. However, a public entity may  provide a separate seven-digit line for the exclusive use of nonvoice callers in addition to providing direct access for such calls to its 911 line.