I map Sensorly passively M through F from Fort Washington to Quakertown. I noticed that once tower PL73XC205 in Fort Washington got marked yellow in the NV Sites Complete forum, I consistently got 5 bars 3G, but was not able to use data for entire days? I just chalked it up to what might happen while the tower was being worked on.
So I guess, if my drive route wasn't already marked in Sensorly for 2G/3G, it would have been picked up along my drive, even though I couldn't connect to Pandora or Sirius until I moved passed the reach of that tower.