This was brought up a couple of years ago and believe it or not, someone posted a US map with names of soft drinks shaded in different colors by regions. Don't know about the rest of the south, but growing up in Texas everything was "coke", like you said. However, in Oklahoma it is called "pop". While attending sporting events and the like, it seems that the word "coke" is being replaced by "soda" here in Texas. Kind of sad.