The AT&T SB67138 + (6) SB67108 four-line corded base and cordless system features DECT 6.0 Zero Blind Slot Digital technology. This technology strengthens the radio signal in areas that normally have a weak signal to the base unit. Each extension handset provides individual voicemail , line status, and message waiting indication. Mobile employees have easy access to push to talk, paging, call transfer and 3-way conferencing, You can choose between standard speakerphone or headset operation. The SB67138 speakerphone base supports 4 lines with 100 name and number phonebook directory, power failure protection and automated attendant. The SB67138 can also support up to 6 AT&T booster antennas / repeaters (sold separately). The repeaters extend the range between handset and base by 900 meters. SynJ Extendable Range Phone Systems SMB employees work in a variety of places, from small offices to the largest warehouses. The SynJ extendable range phone system provides cordless handset extensions, Push-to-Talk functionality, up to a half mile of extended range and mobile page and conferencing.