Manufactured by KelTel, from their website:- “A product marketed for many years by both Keltek & BT (61B). Converts between DC5 2W and a simple telephone. Keltel can supply the original ROLI MkII previously sold by Keltek Electronics and BT as the 61B. The unit is housed in a small standalone enclosure with its own internal mains power unit. Converts from a standard 2W telephone or system trunk port to 2W E&M for connection to a router, mux or radio set. Keltel also supply other products similar to the ROLI MkII operation but in different build styles and with enhanced operation. Check out the AS50, Dual Channel ROLI, Single Channel ROLI, and the EMTEST test unit.”

ROLI == RingOut Loop In