Rescued a Cisco 7942 IP phone from ewaste... now what?

Hi, so like the title says... I'd like to know what I can do with this IP phone. I'm SWE, but I've never really ventured into the realm of infra stuff like IP phones, Asterisk, FreeBPX... etc despite almost doing it thanks to a NetworkChuck video where he setup a thing on a Rpi4. The most telephony stuff I've done is messing around with an Obihai/Polycom VOIP adapter thingy to setup my parents with a free "landline".

Any recomendations or guides out there for this? Is the firmware locked on these? Thanks for any tips!