- DuraFon PSL-BU (PRO, Single-Line) long-range cordless phone expansion base is ideal for an add-on to the DuraFon PRO or DuraFon UHF multi-line system when another port or line is needed- Coverage up to: 12 floors (office / hotel), 250,000 sq. ft. (retail store / warehouse) , or 3,000 acres (farm / ranch)- Expandable up to eight (8) base units- Works with DuraFon PRO or DuraFon UHF handsets (up to 90)