The SPM-4100WTX is our NEW Advanced Technology, Heavy Duty Speaker Microphone Series that features WIRELESS PTT (Push-to-Talk) Capability. Use the compact PTT-4100W Transmitter unit to remotely activate the SPM-4100WTX internal PTT receiver. The SPM-4100 series also features a special 3.5mm jack for use of external accessories such as earphones, headsets and throat mics.