If I remember correctly from the conversation I mentioned above: this is only implementable yourself with a VOIP solution and not an actual phone line?
I really recommend against introducing analog anything into a modern VoIP system in 2018. Better to port your landline's DID to a VoIP service and route it from there. If you need a physical landline looking phone, good quality sip desk phones are $50 (assuming you don't care about huge color screens).
Definitely. End-to-end digital is best for fidelity and reliability. Running your own PBX is another point of failure for a service most people expect very high uptime out of, and opens you up to toll fraud. It's only worth it if you have a lot of phone or want call recording or transferring.
[1] https://www.asterisk.org/products/telephony-interface-cards