When calling 9-1-1 from a cell phone there are issues you must consider that are not present with a traditional home or business phone. Phones from a home or business are routed to the proper 9-1-1 center using a fixed address. A cell phone used in the same home may connect to a tower in another city or county and be routed to a different 9-1-1 center. You may be on a road in Shelby County but connect to a tower across the County line and reach Jefferson County 9-1-1. You might connect to a tower that is routed to the City of Hoover, Birmingham, Irondale, or Leeds.
With the current technology cell phone 9-1-1 calls can not be routed precisely so you may need to ask to be transferred to Shelby County 9-1-1 if you are in the Cahaba Valley Fire District or the Rex Lake Fire District.
This issue occurs all across the country anytime you are near the boundary of two or more 9-1-1 systems. If you make a call from the middle of Shelby County it is very unlikely you will be connected to another 9-1-1 center, this only occurs near a city or county boundary.
For more about wireless 9-1-1 go here: http://www.shelby911.org/wireless911.htm