A university bought a 5ESS in the 80s, ran it for ~35 years, did two major retrofits, and it just kept going. One physical system, understandable by humans with schematics, that degrades gracefully and can be literally moved with trucks and patience. The whole thing is engineered around physical constraints: -48V, cable management, alarm loops, test circuits, rings. You can walk it, trace it, power it.
Modern telco / "UC" is the opposite: logical sprawl over other people's hardware, opaque vendor blobs, licensing servers, soft switches that are really just big Java apps hoping the underlying cloud doesn't get "optimized" out from under them. When the vendor loses interest, the product dies no matter how many 9s it had last quarter.
The irony is that the 5ESS looks overbuilt until you realize its total lifecycle cost was probably lower than three generations of forklifted VoIP, PBX, and UC migrations, plus all the consulting. Bell Labs treated switching as a capital asset with a 30-year horizon. The industry now treats it as a revenue stream with a 3-year sales quota.
Preserving something like this isn't just nostalgia, it's preserving an existence proof: telephony at planetary scale was solved with understandable, serviceable systems that could run for decades. That design philosophy has mostly vanished from commercial practice, but it's still incredibly relevant if you care about building anything that's supposed to outlive the current funding cycle.