Hi,
I assume this is with the GPRS code? I had hoped someone who has actually done this would respond (I never tried the GPRS sniffing code).
Ah yes, I forgot about this ...
I don't know what you run, but it's also completely possible that you just don't see uplinks ... just because the filters are removed doesn't mean you'll see as much UL traffic than DL traffic, the range is still much more limited.
Cheers,
Sylvain