Guys, the weird callsigns you hear SKW88B, Unted916T, and so forth are all normal operating flights, ferry/repos, anything really. I fly out of KSLC and the Denver area quite a bit and hear mainline United, Skywest, etc use these. It has to do with cutting down on similar sounding callsigns where a particular operator has high density ops. They keep the callsign for the duration of the flight though. Thats what I've been told by a friend who flies for SKW.