While an assistant coach may well convey Fergies instruction to the MUFC players, he's probably less likely to convey Fergie's abuse directly to the match officials!
;-)
Incidentally, your post made me check up on the Laws of the Game. When I was refereeing (many years ago) ALL touchline coaching was against the rules. (Even though it happened all of the time, whether on the parks or in professional football). I was surprised to read that the current rule is "only one person at a time is authorised to convey tactical instructions from the technical area".
However a more pertinent rule might be this one:
"The use of radio communication systems between players and/or technical staff
is not permitted".
That would seem to prohibit the use of mobile phones between Fergie and his assistants.
Source:
http://www.thefa.com/...1.ashx/LOTG201011.pdf
Chris