Aside from simply connecting to the Plain Switched Telephone Network (PSTN), PhilTel aims to connect to other, smaller phone networks run by hobbyists and collectors who want to make their phone equipment accessible to others.
PhreakNet is a hobbyist network of phone collectors. If you think of the PSTN acting like an Internet of phones, PhreakNet is more like your home or office Local Area Network (LAN). Think about how at your home you may have many computers, tablets, printers, and smart devices that can communicate and connect to one another. It’s easy to send a document to your printer or grab photos off the computer in your bedroom when you’re sitting in the living room, but if you walk a couple blocks away to a coffee shop you may not be able to do any of these things because you have left your local network. PhreakNet works in a similar manner with hobbyists each running their telephone equipment on one big virtual LAN.
Back in the day, telephone companies would erect buildings called Central Offices to service distinct geographical areas. Telephone exchanges could only hold a certain number of customers, so it would not be uncommon to see a single exchange servicing a county or a dozen exchanges servicing a city depending on population density. Similar to this, each hobbyist joining PhreakNet creates their own exchange using software instead of physically constructing a building. Instead of one phone number on an exchange going to one household, PhreakNet users use these numbers to wire up individual phones, create test numbers, point to recordings, or interface with other telephone hardware.
Similar to your home LAN where computers and other devices can easily communicate information, exchanges also allow for interconnection so a phone on one exchange can easily call up a phone on another. Instead of running physical trunk lines between exchanges like the old North American phone network, PhreakNet leverages VoIP links to connect hobbyist-run exchanges virtually.
Further, just as your LAN devices are somewhat isolated from the Internet (and random people can’t access services within your network unless you explicitly configure things this way), PhreakNet numbers are not directly accessible from the PSTN unless a gateway is dialed into first to gain access to the network.
You can see a full directory of PhreakNet numbers to dial here.