When triyng to run iconv.exe under windows with the VBScript, the arguments don't go to executable.
Set SHL = CreateObject("WScript.Shell")
SHL.Run """iconv.exe"" -f utf-16 -t utf-8 in.txt > out.txt"
I think it's error with quotes but can't find the right way.
.Run starts a process, not a shell. You need a shell for shell's features like re-direction. So:
Dim SHL : Set SHL = CreateObject("WScript.Shell")
Dim iRet : iRet = SHL.Run("%comspec% /c ""iconv.exe"" -f utf-16 -t utf-8 in.txt > out.txt", 0, True)