Hi: we do this regularly with Allen Bradley. It is a straight through connection RS232 to the CPU. Or, using a KE module. It is ESSENTIAL to set the baud rate of the PLC cooms node to match the modem (usually 19200). I am also in the UK, and if you ask for Vince Collis at Westermo tel 01489 580585. Vince has been of tremendous help with all our Westermo applications!