SnarfWare, by Two Dogs, is some promising looking software, but you need to provide the hardware and the signals in the proper way.

NOTE: This is for MS-DOS, of course!

SAsnarfer text file,by Two-Dogs. 3-Feb-96.

 This is just a pre-release of Snarf-ware to see how things are going,
so I can get some feedback. This version (0.8b) is compiled shitty-basic,
which is slow. I'm re-writing it in C to speed things up a bit, so older
PC's can work with it.
   Also for speed, there is no parity checking, so all 5 word repeats are
displayed for you to decide the pair.
   The pins used are 'Celltrack' compatible, as suggested in the 'Snarf-4'
text file that floats around.

  You will need to obtain two lines to feed your PC,
they are CLOCK, and NRZ-Data.
The CLOCK is a 10kHz clock phase-locked to the transmitted 'Manchester' data-
burst received from the handset.
The NRZ-Data is the 'Non-Return-to-Zero' data line, which is the result of
XOR-ing the transmitted data with the 10kHz clock. 

Both of these lines occur within cellphones, all you need to know is where.
Then you need to get the phone to receive the REVERSE control channel.
This can be done by feeding the wide-FM demod' signal from a scanner into the
cellphone, replacing the phones demod line, but this will not work too well
for phones within 50 yards or so, as the scanner may overload with the burst.
Or you can try building your own 10kHz PLL to sync-up with the data using a
4046 or similar, but remember the PLL must be able to lock quickly and have
a narrow lock range, this will help.

  Future versions will include Forward control channel decoding, just so you
can check your hardware, and maybe a parity check.

 Stick any comments in alt.2600 or alt.cell-ph-tech or catch me on #Cellular.
If you have anything that needs it, here is a PGP key. Use it.

Version: 2.6.2i