Using an old Bluetooth-enabled Blackberry as a GPS
Well, if the GSM on the device can be activated and accessed through the BT then you are OK to use it, but I am not sure you will be able to use the BT to control the GPS functionality of your mobile phone.

In order to test this, you may find it easier to use a PC with BT and try to get that working first, if you manage to do that, then implementing BT communication with FPGA is not a big deal, it is a bit over kill, but it is definitely possible.