Ah good memories! Even though I knew nothing about VoIP I installed, years ago, one at my wife's little SME using "RasPBX" (a distro made of Raspbian + FreePBX + Asterisk) running on a... Raspberry Pi 1 (maybe a Pi 2 but I'm pretty sure it was a 1). The Pi was booting from the SD card but everything was running on an external HDD.
I did put six Cisco VoIP phones and all was working fine as long as no more than four phones were used simultaneously (which never happened). It worked for years like that and wife ended up selling her SME with these VoIP phones still hooked to the RPi 1. We warned them that that thing was kinda a hack ; )
For anyone hesitating: it's not hard to set up. Find a provider to get a SIP trunk, configure the thing, backup the config (I just imaged the entire drive), and you're good to go for a very long time.
It's simple, reliable, stuff that usually won't move under your feet.
I did put six Cisco VoIP phones and all was working fine as long as no more than four phones were used simultaneously (which never happened). It worked for years like that and wife ended up selling her SME with these VoIP phones still hooked to the RPi 1. We warned them that that thing was kinda a hack ; )
For anyone hesitating: it's not hard to set up. Find a provider to get a SIP trunk, configure the thing, backup the config (I just imaged the entire drive), and you're good to go for a very long time.
It's simple, reliable, stuff that usually won't move under your feet.