So what is phone phreaking?
"Phone phreaking" is the lost art/science/pursuit/criminal enterprise/etc of hacking the phone system. This is not talking about using computers in any kind of way (or at least they aren't required) but of using the phone system's own features and mechanisms against it. To explain how this all worked, we need to talk about a little history.
So someone asked me in the comments if the DreamPi (a software and hardware device that allows you to bridge the Dreamcast into the internet via its internal modem, using a Raspberry Pi, a USB modem and some magic to create an ISP emulator) would be considered phreaking and I think this is a pretty good addition to this post because it goes in to some of what I wanted to touch on about situating phreaking as a historical era as much as a techological pursuit.
is a dreampi considered phreaking
mostly to trick the dreamcast into an ethernet bridge by being a fake isp to 'dial' into
So the really unsatisfying answer is this: Maybe? The thing to understand is that like most subcultures and hacking or hobbyist pursuits, phreaking was as much about the time, place and environment as it was about the technical nitty-gritty. At its core, as I talk about, phreaking was about hacking the phone system and the dreampi is really about building a super-minimal phone system emulation. Is this phreaking? Maybe!
Remember, there was no real bright line separation; lots of computer hackers were phreakers, and lots of old school phreakers became computer hackers. Look at Bill Acker who was an important figure in open source years after the death of phreaking as an organized pursuit. It's really more about how you want to situate what you're doing technologically and historically.
What about the dreampi and making the DC talk to the Internet interests you? Is it about retrogaming mainly, with the network hacking being something ancillary? Is it about learning about obsolete networking systems? Or is it in whole or in part about exploring telephony? Because that's what phreaking was: Exploring and hacking the telephone system. If that's something that interests you, even as a historical curiosity... Sure! If you want to situate what you're doing in that historical and social context, it could be a form of archaeological phreaking. Or it could not be.
Don't ever let anyone tell you these are purely technical questions; phreaking dissolved into more "conventional" computer and network hacking because the phone system itself dissolved into computer networking and, eventually, the internet, and the social context of phreaking disappeared into modern network and computer hacking along with it. But there are still people whose fascination runs to PBX systems, and the cell networks and so on. The reason they're not usually called phreakers is because the social context is gone, that period of history is gone. But they could be. So could you, if that's where your interest lies.

