When Sanji finds out Mr.3's hut in Little Garden, he answers a call by Mr.0, who mistakes him for Mr.3 himself.
We know that den den mushis look like whoever's speaking at the other side of the line, so Mr.0 (who should know who his subordinates are) should have recognized that it was not Mr.3
Is it maybe a special den den mushi that does not show the likeness of the individual, for the sake of not letting anyone know who Mr.0 is, or is there a different explanation?