My experience from almost a decade ago, mostly in DSL land, is that most customer calls were "my WiFi doesn't reach through the solid steel wall the router is hung against" and "how do I set up my email" and maybe "I lost the password to my WiFi again". WiFi issues were especially bad when 802.11n got finalised but there were tons of "draft n" WiFi devices out there that almost followed the WiFi spec. I still shudder when I see Atheros listed in device manager.

There were things that made the ISP I worked at special, one of them being that we pretty much defaulted to having customers hook up their own DSL, which meant spending a lot of call time helping people who have no idea what an RJ11 jack is install plugs and adapters.

I've also spent a lot of time on "the password I use for my email doesn't work on my Facebook" and "my USB printer doesn't work". People don't know who to call for tech support so they try their ISP. There was also the occasional "the internet is broken" whenever the user's home page had a different theme or design as well, those usually came in waves.

Once the modem and/or router is installed, most internet services Just Work. There are outages and bad modems and the occasional bad software update to deal with, but they're a relatively low call volume compared to what customers call about.