This short paper contains two sections. The first suggests that a callback modem can be replaced by a program in which a caller can specify the phone number to be called. This seems to defeat the very purpose of callback modems, however, which is to prevent an unauthorized user, who may have captured a password, from signing on. The second section reviews some other work regarding authentication protocols that does not seem to relate to the suggestion in the first section. In summary, the paper does not seem to offer any new and useful ideas.