Almost a dead-ringer for the early-model Sharpe HA-10, Koss's PRO-4 ($45) is readily distinguishable by a large knurled protuberance sticking out of the lower part of the right-hand phone. This, in case you've wondered, is a mounting for a "boom-type" lip microphone, for use in speech labs and for communication purposes. (Sharpe and Permoflux also provide facilities for attaching a lip-mike.)