text: Q:
  
  Etymology and usage of 凸待ち
  
  I've seen the internet slang 凸{とつ}待{ま}ち used for "waiting for incoming (Skype etc) calls" pretty frequently, but what is the etymology and usage of the word?
  I've read on other sites that it came from the following:
  
  突撃{とつげき}待{ま}ち → とつげき待{ま}ち → 凸{とつ}げき待{ま}ち → 凸{とつ}待{ま}ち
  
  But why did "attack" come to mean "incoming calls"? And why did 凸{とつ} ("convex") come to be used instead of 突{とつ}?
  Also, can it be used in a more generic sense, i.e. "waiting for an [assault/attack]"?
  
  A:
  
  I figure I may as well try to answer my own question:
  
  The ニコニコ大百科 page for 凸 says this 凸{とつ} comes from that the reading is the same, so I think it's likely it's just that it's easier to input than 突{とつ}. 
  However, I might speculate the popularity of お凸{でこ} may have added to the popularity of 凸{とつ}, and apparently misreading 凸{とつ}待{ま}ち as 凸{でこ}待{ま}ち is a fairly common mistake (before asking this question I thought it was read that way too).
  This page says the meaning of 凸待ち is "waiting for somebody to 'phone attack' them" ("誰かが電凸するのを待っている状態"), so I think that's probably the origin of this phrase. I think it's likely tongue-in-cheek, as a lot of internet slang is.
  
  