Why text messages are limited to 160 characters

Alone in a room in his home in Bonn, Germany,Friedhelm Hillebrand sat at his typewriter, tapping out random sentences and questions on a sheet of paper.

As he went along, Hillebrand counted the number of letters, numbers, punctuation marks and spaces on the page. Each blurb ran on for a line or two and nearly always clocked in under 160 characters.

That became Hillebrand's magic number -- and set the standard for one of today's most popular forms of digital communication: text messaging.

"This is perfectly sufficient," he recalled thinking during that epiphany of 1985, when he was 45 years old. "Perfectly sufficient."

The communications researcher and a dozen others had been laying out the plans to standardize a technology that would allow cellphones to transmit and display text messages.  Because of tight bandwidth constraints of the wireless networks at the time -- which were mostly used for car phones -- each message would have to be as short as possible.

Before his typewriter experiment, Hillebrand had an argument with a friend about whether 160 characters provided enough space to communicate most thoughts. "My friend said this was impossible for the mass market," Hillebrand said. "I was more optimistic."

His optimism was clearly on the mark. Text messaging has become the prevalent form of mobile communication worldwide. Americans are sending more text messages than making calls on their cellphones, according to a Nielsen Mobile report released last year.

U.S. mobile users sent an average of 357 texts per month in the second quarter of 2008 versus an average of 204 calls, the report said.

Texting has been a boon for telecoms. Giants Verizon Wireless and AT&T each charge 20 to 25 cents a message, or $20 for unlimited texts. Verizon has 86 million subscribers, while AT&T's wireless service has 78.2 million.

And Twitter, the fastest growing online social network, which is being adopted practically en masse by politicians, celebrities ...