I researched this a couple of years ago, with some interesting findings.
For max distance you need digital spread spectrum (DSS). DSS phones <font color="red">far</font> outdistance the others. The 900 MHz DSS seems superior to the other frequency bands on the market. DSS phones have a longer range because they are authorized a higher transmit power than non DSS phones.
You also need DSS for maximum privacy from scanner buffs. At a minimum, you absolutely need a phone that has digital voice in <font color="red">both</font> directions, unless you don't mind someone listening to your phone calls (of course, that's harder in the country than it is in the city).
I originally bought an AT&T 900 MHz DSS phone. It had superb range, but it also had an annoying habit of garbling certain long distance calls. I returned it and got another, identical unit. It too garbled some long distance calls.
I was never able to discover a satisfactory explanation for the phone's behaviour, but I did find a number of web references to individuals who had exactly the same experience with that model phone.
I returned the second unit, after getting an AT&T rep to admit there seemed to be some sort of problem.
I then bought a Toshiba 900 MHz DSS cordless. It has been superb, and has about a 1/4 mile range in flat country. I couldn't be happier with it. Unfortunately, Toshiba seems to have dropped out of the cordless phone market.
BTW, some of the non DSS phones marketed as digital are actually digital in only one direction. They are analog in the other, with all its vulnerabilities. You have to be very careful when reading the marketing hype on the box. Some aren't even digital at all.
For example, a couple of days ago I was looking at a phone in the local Wally World. The box virtually screamed, "Digital answering machine and cordless phone combination." A careful examination of the claims on the box revealed that only the anwering machine portion was digital. The cordless phone itself was analog. I watched a couple buy one, thinking they were buying a digital cordless phone.
2.4 GHz and higher phones are getting into the microwave frequency bands. 2.4 GHZ phones compete with wireless LANs for spectrum, among other things, and I personally don't much like radio frequency emissions at that high a frequency right next to my head--theoretically safe or not.
My advice in a nutshell: Buy a 900 MHZ DSS phone from a major name, other than AT&T. If you can find a Toshiba, that would be my first choice. V-Tech would be my second.
SnowRidge