This would be so easy to implement, can it even really be said to be a technology problem?
For those PSAPs that do have NG911 equipment, managing an SMS "call" is tricky because SMS messages are not sent on a persistent connection. Each message requires routing through the wireless network to a selective router which then routes the call to a PSAP, and the PSAP routes the message to a call taker. So somehow subsequent messages need to be able to find their way to the same call taker that handled the first message.
- How do all of the routing points know what "call" each message belongs to?
- How do they know when the call ends?
- What happens when the caller's location changes and the wireless network routes through a new selective router?
- What if a PSAP is busy or offline? Unlike normal SMS, messages need to be re-routed.
- 911 calls need to be recorded. Who is responsible for storing the SMS conversations? Sometimes PSAPs are required by a state to record conversations. If the SMS solution is a web-hosted application, state laws may need amending to allow the application provider to record the SMS conversation.
The wireless network, selective router, and PSAP equipment may each be managed by a different entity, so it requires new laws, standards and equipment to coordinate a 911 SMS conversation correctly compared to normal SMS calls where the number that is being sent to maps to a single subscriber.