Troops often carry their cell phones on training exercises, or even into combat, keeping them connected to family and friends. Units have different policies on cell phone use in the field. Usually, the troops are told to turn them off when they are training, or set them on vibrate. But even when in the field (and within range of cell phone service), the troops often prefer to use their cells, rather than military radios. This is often the case because there are not that many military radios in a unit (maybe one for every 20-30 troops), and often under the control of officers and senior NCOs. Rather than go to one of these people to get permission to contact someone, you can just use your cell phone. This is easier for everyone, and is often tolerated. After all, the army is planning on equipping everyone with a personal radio, so many officers consider widespread cell phone use a sort of test.
Israel is a special case, as reserve troops are regularly called up for security duty. Before cell phones, these troops just left their families and jobs behind while they were on reserve duty, even if it was only a few miles away from home. There was one phone in the barracks, and that was usually only in use when the troops were off duty. Now, many reservists have cell phones, and are constantly using them. Officers and NCOs have had to crack down, either by ordering the troops to leave their cell phones in the barracks while on duty, or enforce an emergency calls only policy. But Israeli reservists, and active duty troops, have even been found taking cell phones into combat situations. Sometimes this is useful, because there are often not enough military radios. But mostly, cell phones have been another headache for officers and NCOs.
Cell phones are changing military life in unexpected ways. When on base, cell phones have proved to be an asset. Its much easer to get in touch with people, and communicate in general. Even warship crews, when in port, make use of their cell phones on board. At sea, the navy uses walkie talkies. However, there are commercial services that connect cell phone users at sea (on cruise ships), via a satellite link, with world-wide cell phone service. The U.S. Navy is working on that kind of capability for users on warships, with restrictions on the link to the rest of the world.