Signing up for a phone line used to mean choosing among styles of telephones, not selecting providers or types of connections. The range of choices -- including smartphones, land lines and Internet phones, or VoIP -- can blur the distinctions among the terminology you use to refer to these options. The term "land line" refers to a specific type of hardwired, non-mobile connection. Although VoIP service can use your land-line telephones, it doesn't constitute land line service.

Wiring a Connection

Traditional land-line phone service uses analog signals carried over copper wiring. You speak into a microphone built into your telephone handset, and the phone converts the sound of your voice into an electrical signal. Because VoIP connections transmit information digitally, calls can run over fiber optic cable that accommodates broader bandwidth and more conversations than copper wire can carry. Even if a VoIP phone system accommodates the telephones you used on a conventional land line, the system includes hardware and software that encodes sound into binary data for transmission.

Shared Bandwidth

When you use your broadband Internet connection to provide the bandwidth for a VoIP phone system, you dedicate part of the information-transfer capability of your online connection to carrying voice calls. That connection diverts part of the capacity you otherwise use to send and receive email messages and files, conduct online research or purchase activity, or view streaming entertainment. If you share your bandwidth with other people, each user faces a reduction in the bandwidth available for traditional online activities. When you view a movie or download large software updates, your phone-call quality may suffer as your bandwidth diverts to other uses.

Powering a Call

When your electric power goes out, a land line offers important advantages over a VoIP system. The same copper wiring that transmits analog phone signals also carries the power to operate the system. That power comes from the telephone company itself, and can be supported by massive generators that keep phone service operational when other utilities fail. Unless you use a telephone with features that require electrical power -- a built-in answering machine, for example -- you retain communications access if a natural disaster leaves you in the dark. Even if your phone does plug in to a wall outlet, it may continue to provide basic dial-tone capabilities in a power failure. A VoIP phone works only as long as its functions receive support from electric power or a battery backup system, typically one you maintain yourself.

In an Emergency

When you call for police, fire or ambulance assistance, a land line conveys your location to emergency dispatchers as well as the details you report in a voice call. VoIP systems handle 911 calls, but they can't determine and send location data automatically. The differences between the two systems can mean a delay in emergency service that changes the outcome of a life-or-death situation. If you protect your home, business or an elderly relative with a system that transmits emergency alerts over the phone, you may be unable to use a VoIP line to connect to your alarm service. Some systems enable you to register your address so that information accompanies a 911 call, but you must update your registration details every time you move.