(b) That's right. The normal rule that acceptance is only effective when communicated to the offeror applies to acceptance by fax or telex. These types of communication are considered instantaneous, so the contract, if any, is made where and when the message is received, not when an unsuccessful attempt at communication is made. In the present case, B's acceptance was not successfully transmitted in time.
Note: Communication by means of fax or telex is somewhat old-fashioned now, but the technology still exists and is used, in particular by financial institutions and merchant ships.
In the case of email, special statutory rules exist to determine when receipt of an electronic communication takes place. In terms of the legislation it depends on whether the person to whom the communication was sent has designated an information system (such as an email address) for the purposes of communications. If so, the receipt takes place when the communication reaches that system. If not, the receipt takes place only when the communication comes to the attention of the addressee.