I run NetBSD on a tiny Neoware box with a flash disk. It does all my MacIP, ADSP, DHCP, routing and DNS forwarding.
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The modem typically was a computer. Often a tiny little thing that handled the Hayes commands. Unless it was a manual dial, eg with acoustic coupler!
If you have a dial up account, you still can still do the MacPPP/modem thing. If you don't, you have to interface with the network connectivity of today.
At the same time, try and play your 33 RPM LPs on your BluRay.