Alcatel VT 258 portable terminal
The VT 258 was a portable terminal with a monochrome monitor, qwerty keyboard (including numeric keypad and terminal keys), and integral 2400 baud modem.
The modem was BABT approved which meant that it could legally be connected to the UK telephone network.
It has a 5 pin DIN socket on the back which may be an serial connector (possibly RS423).