To my knowledge, there is no special back channel through which your cell phone will transmit GPS data to the dispatcher when you place a 911 call. The telco will always have access to cell tower triangulation data, which can be shared with 911 services (or law enforcement), but in general they are not being fed GPS or WiFi geolocation from your smartphone OS's location service (unless I just don't know about it).

To get that kind of data from your OS to a 911 dispatcher simply by placing a call would be to concede the ability for that kind of data to be leaked over telephony at all, or otherwise constantly uploaded to telcos/authorities.