They don't have better frequency range, they just have the cellular bands unblocked. Why you want to listen to analog cell phone calls is beyond me.
How did you pick up digital mobile phone conversation I'm curious? Well, you COULD.. you'd just be hearing digital noise, because you have no way of decoding the stream? Not to mention phones that use spread-spectrum techniques and frequency-hopping that'll keep you from listening to any full conversation.
When new scanners go through the FCC, the only way they can be certified is if they cannot be modified through any simple means (jumpers/firmware, etc.) to open up the cellular band. Older scanners are known to have very simple modifications.
I'd second the call for checking out RadioReference.com.