Roundhouse Zero Six
From The Stargate Omnipedia
Radio call sign used by John Sheppard in a delusional state. Sheppard believed himself to be in his past, deployed to Afghanistan and attempting to reach his base of operations -- code named "Arc Light."
KEY EPISODE
Phantoms - In his attempt to bring Captain Holland to safety, Sheppard uses the call sign "Roundhouse Zero Six" to communicate with "Arc Light."