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I'd like you to call out a friend for me.
Literal
Friend [object-を] call-out-[receive-てもらいたい]-[explanatory-んです].
A roundabout polite request. ~てもらいたい ('want to receive the doing of X') expresses 'I want someone to do X for me.' Combined with 呼び出す ('to call out, summon'), it asks for someone to be called over. The んです framing is typical of polite self-explanation in requests.