Yay! I managed to compile the above module with zgcc2 and once I did a modprobe, my bluetooth GPRS connection worked like a charm. So, I can assert that for older bluetooth-enabled Ericsson phones (T68i and older), you have to run the kernel module fix because of a IP framing error in the phones' firmware. Note that this does not fix IRDA connections with Ericssons though.
Incidentally, I tried to 'make zImage' using zgcc2 but I had a line parse error in stdio.h (are the zgcc2 include files somehow different from typical cross compilers?). I skipped that step and therefore ran 'make modules' without a modversions.h file. Since my Z did not complain about kernel versions during modprobe, I guess my compiled module is ok. But I wish I could fix the stdio.h error and finish compiling my own customised kernel image. Can anyone help?