I remember in the good old bad old days of the UK, British Telecom launched their Home Highway services which was primarily their ISDN service. They did however have a form of bonded dial-up (usually two lines, but theoretically could support more) which cost a fucking fortune - usually two lots of line rentals; two lots of ISP service packages; and a fuck you fee for wanting to bond them.

Outside of real niche use cases like contingency lines or short term mediumband requirements, I don't think it saw great popularity - particularly when ISDN was expensive but comparatively cheaper.

668kbps though, fuck me. That would have been mindblowing at the turn of the century.