An adapter (400) for a portable land mobile radio (LMR) transceiver system (414) where the LMR includes a push-to-talk (PTT) transmitter control system. The adapter includes a tip-ring-sleeve (TRS) type interface connector (402) configured to accept a plug (101) from a standard mobile phone headset. An adapter circuit (401) is configured to detect a momentary actuation of an answer/end switch (201) of a standard mobile phone headset when a TRS plug of the standard mobile phone headset is inserted in the interface connector (402). The adapter circuit alternately latches a PTT input of the LMR transmitter control system in either a transmit active state, or a transmit inactive state, in response to actuation of the answer/end switch of the mobile phone handset.