In response to a report that incorrectly quoted AT&T Mobility CEO Ralph de la Vega as having promised tethering support for the iPhone by the end of this year, a company spokesperson has cast doubt onto the prospect of tethering in 2009. 9to5Mac, citing Cnet—the source of the disputed quote—wrote in a story that AT&T had promised tethering support by the end of 2009. It soon received an email from an AT&T spokesperson requesting…