This depends on the area of the Country that you live in. Many of the larger ISP's do provide PC to phone services, but it is not available in all areas.
Yes, Skype offers PC to phone services for a small fee. Their PC to PC services are free however. This and other information can be found at their website.
The ISP provides internet in many ways. Most common method is through telephone lines.Internet connection speed can generally be divided into two categories: dialup and broadband. Dialup connections...
There are nearly 7,000 ISPs in the United States alone. While some of them do supply 24 hour customer service, the smaller companies are likely to only staff call centers during business hours.
According to Wikipedia, the first company to offer dialup service to the general public was "The World" based in Brookline Massachusetts. Still in operation today they began in 1989..