SLC is (was) “Subscriber Line (or Loop) Concentrator” which serves a neighborhood. It has changed a lot since it got that name decades ago. Before I upgraded to U-Verse my voice phone was analog on a copper twisted pair all the way to Menlo Park while my DSL was 3 Mb/s over just 1000 ft of copper to the SLC where it connected to the fiber. Now analog voice is just to the little box in my living room and the rest is VOIP (voice over Internet), which I have not seen fail yet. With U-Verse the 1000 ft of copper carries the 15Mb/s digital traffic which serves both Internet access and VOIP.
There is a theoretical drawback to this scheme: When power fails for more than 5 hours the D/A & A/D function in my living room fails and no more voice or digital! The power went out once for six hours since it was installed. Cell service works well enough to bridge these gaps. With the older DSL service failed immediately upon power failure but voice continued until backup power at the SLC expired.