Hi!
I do not know, if it helps you but just in case..
I developed a PIC-"filter" of NMEA-messages. Pic12f629 (INTRCIO mode) monitors GPS (Falcom JP7 but this should not be important) output stream and when it finds a $GPRS message with no receiver warning (got sattelite fix), outputs it in preformatted form via bit-banged RS232 at 4800 bd (if PIC-s pin "enable" - see code comments) is HIGH. Since i am an assembly language fan, it is written in such but ready to burn .hex is also provided. Source commented in english.
Download: http://parsek.yf.ttu.ee/~felc/gps.zip