CLT - has free wireless thruout airport. Booth located outside the biz center for free. the biz center also has hardwired booths, but there is a fee. (very reasonable, and the boots are in a room that is soundproofed in you prefer quiet.) Or there are lots of rocking chairs that have plugs nearby that can be used. All are located on the gate side of security.
GSP - One of the concourses used to have them at the top of the escalator at the gates. It is the concourse I rarely use, so am not certain if they are still available.
AVL - currently being installed. Gate side of security.
LGA - US concourse.