Senate Antitrust Subcommittee Chairman Herb Kohl , D-Wis., wrote to executives of the four largest wireless telephone companies on Tuesday asking them to justify sharply rising rates for customers to send and receive text messages. The letter went to Verizon Wireless, AT&T, Sprint and T-Mobile, which collectively serve more than 90 percent of the nation’s cellular phone users. Since 2005, the cost for a consumer to send or receive a text message over each service increased by 100 percent, Kohl said. Text messages were commonly priced at 10 cents per message sent or received in 2005 and as of this month's end, the rate per text will have doubled to 20 cents on all four carriers. Sprint was the first carrier to increase the rate last fall and its rivals have matched the price hike. The change "does not appear to be justified by rising costs in delivering text messages," Kohl wrote. "Text messaging files are very small, as the size of text messages are generally limited to 160 characters per message, and therefore cost carriers very little to transmit." He also expressed concern that it appears each of companies has changed the price at nearly the same time with identical increases. (Photo Credit: eron_gpsfsr via Flickr) Follow the jump to read Kohl's full letter. --------------------------------------------------------- September 9, 2008 Lowell McAdam President and CEO Verizon Wireless Randall Stephenson Chief Executive Officer AT&T Dan ...