Cell phones have limited range and rely heavily on the cellular network to make a connection. If you leave your carrier's covered area, you won't be able to connect -- unless you have access to an alternate communications method such as Wi-Fi.
QuickStudy: Why your cell phone won't connect
Why cell network coverage isn't always seamless and can be inconsistent among different carriers.
Computerworld - It happens to everyone: You try to make a cell phone call and find you have no service. What's the problem? The device in your hand is more powerful than a full-blown computer from just a few years past; why can't it connect?
Unfortunately, computing power doesn't relate directly to connectivity. Cell phones only work over short ranges and can't transmit more than about eight miles. Most urban and well-populated areas have plenty of cell sites, so coverage isn't a problem, but sometimes there's no cell service within range.
Cellular networks use a series of base stations, each covering a given area known as a cell, and these cells are designed to overlap so as to provide total coverage for a given geographical area. When you switch your phone on, it connects to the nearest base station; as you move from place to place, you may get closer to a different base station, and the network automatically switches your phone to the new cell. But if a base station is already working at full capacity, it can't accept your signal, and the result is a dropped call. Your phone just won't work in that place at that particular time. Dropped calls can also happen in areas where cells don't overlap.
The fact is, the extent and quality of service, and the degree of coverage from various carriers, can differ dramatically from one area to another. People who change carriers (perhaps to get a specific device, like Apple's iPhone, which requires AT&T service) might find that their ability to make specific connections changes significantly -- for better or worse.
U.S. carriers use two fundamentally different types of cell phones: GSM, the generally accepted international standard used by T-Mobile and AT&T; and CDMA, the technology used by Sprint and Verizon. This difference doesn't prevent you from calling or connecting to another cell phone that happens to use the other system, but it can affect the available coverage in a particular area. GSM phones might operate on several different sets of frequencies; if you're in Europe, your your U.S. GSM phone may or may not work -- and even when it does, it may connect differently (and at different calling rates) than you were expecting. In fact, for international travel, it may be significantly cheaper to rent a phone at your destination; the major disadvantage is that you'll have a different phone number.
If you can't make a cell phone call, what about the other communications modes that your smartphone may support -- 3G service (including WiMax), Wi-Fi Internet access and text messaging? Whether you can use them is a good question, and the answer is a qualified "maybe." If you can't access a cellular base station, you probably can't send an SMS text message, either. But you might be able to get totally separate Wi-Fi access and use e-mail. 3G connections are designed to offer data transfer speeds and capacities that are significantly greater than those available with basic cell connectivity. And depending on the flavor(s) of 3G that your phone and your carrier support, you can sometimes communicate via this method when the standard cell connection doesn't work. As always, just try it and see.
Kay is a Computerworld contributing writer in Worcester, Mass. Contact him at firstname.lastname@example.org.
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