I learned to play from the Moldvay Basic rulebook. When I go upstairs after posting this message I'll see what it says about the role of the caller!
Page B4: "To avoid confusion, the players should select one player to speak for the entire group or party. That player is named the caller. When unusual situations occur, each player may want to say what his or her character is doing. The caller should make sure that he or she is accurately representing all the player characters' wishes. The caller is a mediator between the players and the DM, and should not judge what the player characters should do."
Page B19: "One player should be chosen to tell the DM about the plans and actions of the party. This player is the caller. The players may tell the DM what their characters are doing, but the game runs more smoothly when the caller relays the information. The caller should be sure to check with each member of the party before announcing any actions (such as "We'll turn right" or "he thief will check for traps"). The caller is usually a character with a high Charisma score, and should be near the front of the party, where the character would be able to see what the DM describes."
Page B63: "caller - the player who normally tells the DM what his or her party will do, based on what the other plaeyrs tell him or her."
Cheers!