I have been in a number of games where a player pretends to be Skyping / communicating outside of the game in order to get someone else lynched and wanted to know whether this was illegal / reportable as cheating.
In particular, I've seen this used as an Executioner tactic where the Executioner says he has been Skyping with others (unidentified usually) and therefore, he knows that [Target] is Mafia or Triad. Although the town often grumbles about the player cheating, they nevertheless end up lynching the Executioner's target, which of course is revealed as town. Then, the Executioner says something to the effect of "I fooled you guys -- I wasn't Skyping, but thanks for the win."
This seems like a pretty sketchy / questionable tactic to me given it involves pretending to cheat outside of the game in order to influence the town -- i.e. the fake lead has nothing to do with anything the player has done in the game whatsoever, but instead plays off of cheating. However, in many cases, the player in question probably wasn't actually Skyping -- that's the weak defense I've heard from users of this tactic at least. Personally, I don't like it and think it's illegitimate, but wanted to get the official mods' take on the question.