Form of dialogue often expresses otherwise hidden characteristics of the speaker. At the play's beginning, John does most of the talking—and most of the interrupting, showing his dominance over Carol in conversation and his comfort in his role as lecturer. John talks almost exclusively, with very little input—he does not place importance on the other person in the conversation. He fills his lectures with overly elaborate words and academic allusions, for which Carol constantly asks clarication.
More so, however, form can show the exchange between two people in conversation. In the first act, few sentences are completed, and the characters are constantly overlapping each other for an effect that is more talking at that communicating with, trailing off before any meaning is actually conveyed. Carol can get in at most a few words before John assumes her meaning; there is an attempt at communication by Carol, but it is not happening between them. In the second act, both characters speak more freely, Carol expressing her points and John only quieting her with a long, rambling speech reminiscent of act one. Whether or not the reception is there on either end, both parties are allowed more free expression. Finally, by the third act, Carol assumes John's original role, constantly interrupting him and not really listening to what he is saying. His expression is being limited because of Carol's power role, and so true communication is still not taking place.
In a play which has many of the Greek unities—at least, the restrictions on setting and story—Mamet uses the telephone as a sort of modern deus ex machina. It doesn't simply ring incidentally; rather, when the telephone rings, it is either to communicate something which furthers the story along, to give one of the characters a break in an otherwise heavy conversation, or, more often, to do both. The telephone rings many times in act one, alternately Jerry and Grace attempting to lure John away from his talks with Carol. This places importance on John's house purchase and makes it more human and pressing—it is not merely that he is buying a house, but that he has people for whom this house means quite a bit. It also indicates that John has normal human relationships, with people who care for him considerably. John's reaction to the first act's phone calls also make the play possible; if John had run off with the opening phone call, none of the problems would have happened.
Grace's call in the second act serves as an opportunity for Carol to regain her footing—her charges before the tenure committee have given her the upper hand in the power struggle she perceives between her and John, but John's innate power and his strong rhetoric is turning the tides. Until, that is, the phone rings; his flow is interrupted, and she takes the opportunity to close the discussion. The first phone call of the third act sets up the second, corroborating John's story that he has not been home in days and so has not communicated with anyone close to him. Finally, it is the second phone call, informing John that he may be charged with rape and battery, which tips him over the edge into action. This not only interrupts the conversation, it gives Carol an opportunity to comment on John's treatment of his wife. With all this new information, John is overloaded, and lashes out physically. It is important that Mamet does not note the ending of the final phone conversation or include John hanging up the phone. Instead, the possibility is open that John is so upset that all else loses importance and that he enters a mental zone where all that exists is the two of them.
Carol never makes a move on John; she always walks away, calls for help, etc. John, however, is physical with Carol once in each act, to increasing degrees of violence. John's actions are never contrived, however. When Carol is upset, he naturally, without thinking, moves to comfort her. When she tries to leave, he sees no alternative but to restrain her. Finally, when he cannot communicate his anger or impose his opinion in any other way, he beats her. John is a man comfortable with the possibility of his physicality, not awkward within his skin. It is unclear whether expressing himself physically is within or without the bounds John perceives on his actions. It seems obvious that he considers his embrace of Carol not only natural but right, but his struggle to regain composure after beating her reveals that, in his mind, the limit for acceptable action falls somewhere in between. Carol's reactions show her perception of the boundaries as fairly similar, oddly enough, and when John moves to comfort her, she counters physically, moving away. His grabbing is met with a cry for help; what may have been pushing the boundaries for him is not best met with physical resistance from her, as she intends to always work within the limits, crying for help instead. Finally, she must simply take his beating since any counteraction would be improper and detract from the oppressive role in which Carol has cast John. She never crosses into desperation, and so her physical actions are always carefully within the bounds of what she considers proper; she is careful to play her own role and let John fall into the one she wants him to play.