T1 used high quality lines, not shared with others. There was often a high cost to getting it installed because they pulled a new line. ISDN was around for a while with 128k and even 256k, running on ordinary lines. My household got its first taste of "always on" internet with ISDN around 1995. It was not just faster and symmetrical, but it was a surprising change in behavior when you did not need to dial in.
DSL was more modern modulation technology than either T1 or ISDN, with full use of DSP not simply equalization. It ran a lot faster for homes, though with slow upload speeds. A lot of cable modems are like that due to several generations of DOCSIM that depended on a trick to go upstream below a filter that kept everything downstream running above 50MHz, so the upstream was not only at a lower bandwidth with more interference, but it was also shared at the first distribution box.
So, DSL is definitely the answer to Xebec's question and over 25 years old in field deployments.
A tidbit on DSL in the
last mile. T1/T3 may go for many kilometres. DSL, while originally envisioned to go the same, only went for a few KMs to DSLAM, often in the same building. DSL had very poor survivability crossing any analog landline hardware, but analog phone boxes mostly went extinct in the 200X anyway.
If you have a landline, it's mostly digital these days. The digital box will be either in the telecom closet in the building, or on the phone pole somewhere. So, it made little sense to provide DSL, and not digitise the phone switch boxes at the same time.
The real reason DSL held on for so long at all is that phone companies were almost forcefully subscribing everyone onto DSL just to keep landline subscribers around, because they knew 3G will destroy the landline service.
So people just had to pay for a landline they did not use anyway, and phone companies made tons, and tons of completely free money on those landlines which sat unused. The ISP guy I know tells that a double digit of any phone company income is just unused connections, which people get for "free" with an apartment, or an office.
But a decade passed, and people realised the absurdity of the situation: you have massive amounts of fibre coming to the building, or neighbourhood, but then you turn it into low grade copper, just to use an over the top copper modem over it, that does every DSP trick in existence to pull SNR. And then, you again turn it into fiber, or UTP5 ethernet. So, expensive DSLAMs and modems flew out of the window.
