This was reported tonight on local news:
A ill person called 911 for help from his cell phone. The person lived on the border of two counties. The cell phone call went to the wrong county's dispatcher, who sent an ambulance to the address in the wrong county--the address existed in both counties. It took 25 minutes until they unravelled the mistake, but then it was too late.
(I may learn more details tomorrow in the paper. I don't know exactly what the caller told the dispatcher or why the town names got confused. This sort of thing has happened before with county dispatchers and addresses that are duplicated.)
I myself live near the border of two counties (actually a state border). Cell phone calls are almost always answered by the other county, but they immediately connect the call to the proper dispatcher. One time I saw a fire across the border and was able to report it via the local 911 who said they'd relay the information to the other county.