SunnyR9 this issue is NOT affecting all users. It is not however carrier dependant as killhippe suggests. Apple changed the options so that instead of just an enable 4G toggle in the cellular/mobile (dependant on your language settings) menu, a new sub menu has been created entitled voice/data that then gives you an enable 2G toggle, enable 3G toggle & an enable 4G toggle REGARDLESS of carrier. This is so that you can limit which signal bands your device searches for (providing the HARDWARE) is capable, so that if, for example, your carrier don't provide you with a 4G service, you can stop your device from searching for a 4G signal & save battery. It also brings back the enable 3G toggle that was lost if you bought a 4G capable device.
To reiterate, this is not affecting all users, some have downloaded the new software without incident, but this is an option that should be available to ALL users of iPhone 5 & above, but for some reason has not been included in every download. Those of you who have the new menu, great, lucky you. Those who don't, do not worry Apple are working on a fix. Those of you who do t know any better (killerhippie) please stop stating that it is a carrier dependant issue when it is not! 4G coverage is carrier dependant, but the ability to enable your device to connect to a 4G network is most certainly not.