is automatically routed to the most suitable PSAP. PSAPs can be subject to changes including new contact information and changing coverage area. Commercial products exist that purport to keep pace with these changes and allow the telecommunications operator to associate numbers with the relevant PSAP based upon their physical address associated with that number. In other countries, this is the responsibility of other types of local government, and the particular setup of the telephone network dictates how such calls are handled. There is also now the ability to answer text messages at some PSAPs, which is useful in areas where weak signal strength due to distance from the nearest cell site causes fringe reception, resulting in blocked or dropped calls. Since SMS messages only require an instant to send, a brief peak in radio propagation (such as a sudden favourable shift in multipath phase alignment) is often enough to get a message sent. Text messages are also useful for the deaf or speech disabled, as it does not require a TTY device. NENA i3 Solution The National Emergency Number Association (NENA) long-term solution for emergency calling, referred to as the i3 Solution, assumes end-to-end Internet Protocol (IP) signaling from the Voice over IP (VoIP) endpoint to an IP-enabled Public Safety Answering Point (PSAP), with callback and caller location information provided to the PSAP with the call. While the i3 Solution assumes end-to-end IP connectivity, and it is expected that an increasing number of PSAPs will evolve to support i3 functionality over time, legacy PSAPs must continue to be supported as originating networks and the Emergency Services infrastructure migrate toward IP. Legacy PSAP Gateway The Legacy PSAP Gateway is a functional element of the i3 Solution architecture that supports the interconnection of the i3 ESInet with legacy PSAPs. The Legacy PSAP Gateway is expected to provide interworking and other functionality necessary for emergency calls routed via an i3 Emergency Services IP Network (ESInet) to be delivered to and handled by legacy PSAPs without requiring changes to legacy PSAP Customer Premises Equipment (CPE). Calls routed via an i3 ESInet and delivered to a legacy PSAP must undergo signaling interworking (i.e., at the Legacy PSAP Gateway) to convert the incoming IP-based (i.e., Session Initiation Protocol [SIP]) signaling supported by the ESInet to the traditional Multi-Frequency (MF) or Enhanced Multi-Frequency (E-MF) signaling supported by the legacy PSAP. Functionality must also be applied by the