Later I went to a library (only 2 stories but with more comfortable sitting areas) and was able to get what I strongly believe is a 3G signal along with something a little lower that may be GSM.
I'm still hard at work studying DSP in my spare time. I found a bug in the Python scripts I released. I shouldn't have used the radians() function. That t variable in sin(2*pi*f*t) was just time, not time as degrees.
While there's not much I can currently do on the cell phones project, I can still take IQ recordings and add them to the cellphones page. Taking my equipment in public today has allowed me to record some 2G GSM, which I don't really have where I live.
While I may never be able to get much from a cell phone downlink, I hope to at least see some indication that I'm close, even if it's just a PSK/QAM constellation. So far the chances are looking slim, but I'm not too discouraged because this is how the HDTV experiment began. At that time I had searched for months without success. It really looked like there was no possible solution to watching TV on the SDRplay, but I wouldn't accept defeat. Of course I am realistic and if the TV issue had been a hard limit in the SDR's chips then I would have quit. I only continued because I could see that it just needed a software solution.
Anyway, my efforts ended up paying off and I'm surprised at how popular my TV post continues to be. It shows that almost anything is possible with enough effort. I hope my cellphones/3G project will be just as rewarding.