His move marks the second time he has resigned from Viacom Outdoor - almost exactly two years ago he left to join More Group as the commercial director of its Adshel division. However he returned to Viacom Outdoor just five months later, in an expanded European role.
Moug left the company last week to set up his own business, which will focus on management development and sales training.
His former employer has become his first client, having hired him on a three-month basis to train and nurture its staff's sales skills.
Moug's deputy, Laura Doughty, replaces him and takes on the role of national sales director, while Marie Clark has been elevated to the position of regional sales director.
Viacom Outdoor's joint managing partner, Clive Punter, said he had restructured the sales team beneath Doughty and Clark to strengthen its management.
"We are now totally focused on our clients needs and we don't intend missing a heartbeat, he added.
Alison Reay, the sales director on the ill-fated XTP system, is also leaving Viacom Outdoor, having taken a senior sales role at Yahoo!. She has been at the company for four years and leaves at the end of the month.
Viacom Outdoor put the XTP system on hold last month following a series of problems, which culminated in the collapse of one of its technical suppliers. However, it is expected to resurface sometime in the future.