I had DreamKey 1.5, IIRC in the UK you had a choice of 2 numbers or something, but it had to go through Sega's server.
They came with a 33.6k modem as standard, but in Japan a handful of Ethernet cards were sold (ultra rare now). They also had a serial port with a proprietary plug, with some games capable of linkup.
There were some very good games, and 50 Es for a working one with some games is about right.