If you wanted to play what is basically a LAN game today, you would have your modem directly call your friend’s modem for only the cost of the phone call. We did this for Doom “deathmatches”.
You could dial into a server for multiplayer but you would typically have to pay for that access because the server’s owner was paying for fancy multi-line service that could handle all the connections at once.
Kevin Mitnick! He died last year… Whistle F to pay respects. He was an early practitioner of SIM cloning, which is an even bigger deal today because criminals can do it to receive people’s two-factor authentication codes and then get into their bank accounts, etc.