Although I'm not surprised at the results of a recent Stanford study regarding our dirty cell phones, I am a bit shocked at just how gross they can get. A group of Stanford University students recently discovered that our cell phones are 18 times dirtier than a toilet handle. That's pretty disgusting. Of course, if you take into account how many different communal surfaces our hands touch — door handles, elevator buttons, bus hand rails, etc. — then how many times we check our phones before washing our hands, you can see how the germs can really start to add up.
Using a 40/60 alcohol to water mixture on solid phone parts and keyboards should be OK for your devices (use a damp cloth and/or cotton swab for small and hard to reach places), however you do not want to use any sort of alcohol, ammonia, or harsh cleaning agent on touchscreens. In these cases, it's recommended that you use a damp water cloth to wipe down your screen, or try my favorite, iKlear wipes ($15). iKlear was made for Mac products in mind, but is safe for LCD screens, touchscreens, and multitouch displays, and comes with an antimicrobial to kill bacteria and fungi.