Reply #6: Some ISPs

[necso]

accept DSL from a third party DSL provider. (I checked into it when I switched -- which was as soon as it was available.)

Internet access typically amounts to:
1) Some physical connection, which your (nominal) ISP may not play any part in providing;
2) An IP address (or "part" of one);
3) Routing services;
4) Email account(s);
5) An account(s) on some server(s) for webspace, account management, "special" services, etc; and
6) Support.

Some ISPs will let you keep #'s 4 and 5 (for some fee), while accessing the web in whatever way you want.

Support is trickier. If you have "split" services, then you will have to rely on split support.

However, DSL tends to be less of a problem that does dial-up, although I have had to learn to recognize a temporary problem or two -- and not waste my time calling support like a zillion other customers will be doing.