Call back number provisioning for emergency call services

1. A communication system comprising:

a call processing system configured to receive first call signaling for an emergency call indicating a user identification for a caller, process the user identification to determine a call back number for the caller, insert the call back number into the first call signaling, and transfer the first call signaling to an emergency information system;

the emergency information system configured to receive the first call signaling from the call processing system, process the first call signaling to determine a destination for the emergency call, generate second call signaling indicating a key and the destination, generate a database message indicating the key and the call back number, transfer the second call signaling to the call processing system, and transfer the database message to a database system.

2. The communication system of claim 1 wherein the emergency information system is further configured to determine the call back number from the first call signaling.

3. The communication system of claim 2 wherein the first call signaling comprises a session initiation protocol (SIP) invite message.

4. The communication system of claim 3 wherein the call processing system is further configured to insert the call back number into a privacy asserted identity field of the SIP invite message.

5. The communication system of claim 1 wherein the emergency information system is further configured to process a privacy asserted identity field to determine the call back number.

6. The communication system of claim 1 wherein the call processing system is further configured to transfer the key to the destination and wherein the destination is configured to transfer a query indicating the key to the database system and wherein the database system is configured to return a response indicating the call back number in response to the query.

7. The communication system of claim 6 wherein the database system comprises an automatic location identification (ALI) database system.

8. The communication system of claim 7 wherein the destination comprises a public safety answering point (PSAP).

9. A method of operating communication system, the method comprising:

in a call processing system, receiving first call signaling for an emergency call indicating a user identification for a caller, processing the user identification to determine a call back number for the caller, inserting the call back number into the first call signaling, and transferring the first call signaling to an emergency information system;

in the emergency information system, receiving the first call signaling from the call processing system, processing the first call signaling to determine a destination for the emergency call, generating second call signaling indicating a key and the destination, generating a database message indicating the key and the call back number, transferring the second call signaling to the call processing system, and transferring the database message to a database system.

10. The method of claim 9 further comprising, in the emergency information system, determining the call back number from the first call signaling.

11. The method of claim 10 wherein the first call signaling comprises a session initiation protocol (SIP) invite message.

12. The method of claim 11 wherein the SIP invite message includes a privacy asserted identity field and wherein the call back number is inserted into the privacy asserted identity field.

13. The method of claim 9 further comprising, in the emergency information system, processing a privacy asserted identity field to determine the call back number.

14. The method of claim 9 further comprising transferring the key from the call processing system to the destination, transferring a query indicating the key from the destination to the database system, and transferring a response from the database system to the destination in response to the query wherein the response indicates the call back number.

15. The method of claim 14 wherein the database system comprises an automatic location identification (ALI) database system.

16. The method of claim 15 wherein the destination comprises a public safety answering point (PSAP).

17. A computer storage system with machine-readable processing instructions stored thereon for operating an emergency information system, wherein the processing instructions direct the emergency information system to:

receive first call signaling from an interface wherein the interface received the first call signaling from a call processing system, wherein the first call signaling indicates a call back number of a caller, and wherein the call back number is determined in the call processing system based on a user identification for the caller, process the first call signaling to determine a destination for the emergency call, generate second call signaling indicating a key and the destination, generate a database message indicating the key and the call back number, transfer the second call signaling to the interface for transferring to the call processing system, and transfer the database message to the interface for transferring to a database system.

18. The computer storage system of claim 17 further direct the processing system to determine the call back number from the first call signaling.

19. The computer storage system of claim 18 wherein the first call signaling comprises a session initiation protocol (SIP) invite message and wherein the software is operational when executed by the processing system to direct the processing system to insert the call back number into a privacy asserted identity field of the SIP invite message.

20. The computer storage system of claim 19 wherein the processing system is configured to process the privacy asserted identity field to determine the call back number.