One of my first Radio Shack portables was able to pick up cell phone calls, and I did hear some interesting conversations involving some of my neighbours. It was a long time ago, but in those days you could hear what I think they called images, so I could also pick up the DEA on a channel that I couldn't directly programme into the scanner. You know what? Cell calls are BORING! There are husbands calling their wives (What's for dinner? Oh. What do you want to do tonight? I don't know, what do you want to do tonight?). Businessmen dissing their partners. Hey, not just BORING, also DEPRESSING! Used to be able to pick up cordless phones a lot too. Same thing. My boss and next door neighbour. For months I heard his wife saying insulting things about me and my family, about her husband and his family. But I didn't say anything to him until one day I arrived home and found him moaning because his wife had taken everything in his house, put it in a truck, and took off. Even then, you see, having heard almost everything didn't do anybody any good.
Theoretically, it should be possible but why bother? What use is it?