Are free-texting apps legal?

How Conventional SMS Texting Works

To understand how free-texting apps work, you first have to understand how phones send and receive text messages in the first place.

If you're a Millennial generation member accustomed to using that ubiquitous gadget in your pocket to buy sneakers, watch movies and play Angry Birds, it may come as a shock to discover that when mobile phones first became widely available in the 1980s, they were initially intended just for -- gasp! -- talking. (They also were the size of bricks and cost thousands of dollars.) Then, a German electronics whiz named Friedhelm Hillebrand realized that in addition to the radio channels upon which mobile phone networks relied to send out voice signals, there were also second channels that were largely unused, except to send some technical instructions to mobile phones about things such as reception strength. Instead of wasting that bandwidth, Hillebrand got the idea of using it to allow users to send short text messages to each other. SMS, which stands for Short Message System, was born [source: Milian]. The first-ever SMS message -- "Merry Christmas" -- was sent over the British Vodafone network in December 1992 [source: Mobile Reference].

But texting took awhile to take off. Initially, phone companies would only allow subscribers to send messages to other subscribers inside their networks -- because it took them awhile to figure out how to charge fees for messages that came from outside their networks [source: Hillebrand]. And it was difficult to tap out messages on numerical keypads, until a Seattle-based company called Tegic invented a program, T9, that predicted the rest of a word after a user had typed a few letters [source: Gow and Smith].

By the early 2000s, though, the barriers had begun to fall. In 2003, it became possible for the first time to send SMS messages to another user on any mobile phone network in the U.S. or Canada [source: Gow and Smith]. The Cingular mobile network helped popularize SMS by encouraging users to vote via text for their favorites on the TV talent contest "American Idol" (and, of course, rack up charges in the process). By 2006, Cingular alone was transmitting tens of billions of text messages on its network [source: Mobile Reference]. By 2011, Americans were sending about two trillion text messages, and texting was generating about $20 billion in revenue for U.S. mobile carriers [source: Wortham].

By that time, though, another revolution -- smartphones equipped with Internet access and more powerful microprocessors that enabled them to function as pocket computers -- had also arrived.