DTMF Microphone for FTM-350 FT-8900 FT-8800 FT-7900 FT-2900 FT-1907 FT-1900 Internally, this is the same microphone as the MH-48A6J, except that it has thetelephone-typealphabet printed above each numbers (2 - 9). This lettering is to assist with APRSĀ®/Packet use.