I did support for a tiny ISP in 1999 [1], we had to have people remove and reinstall that from time to time. Many people could just do it, but I remember one customer I spent maybe two hours on the phone walking her through it. Would put her on hold when another call came in, and then check back with her. Eventually got it all settled.

[1] we had one T1 for internet and one T1 PRI for the modem pool, and outsourced to MegaPath for out of area dialup, and then shunted all the customers to that when the PRI stopped working