"I am asking if the telephony is totally outside and has no impact on the interent.. or viceversa... "
Well, the answer depends on what they using. For the past several years, phone over cable systems were switched digital phone systems. The cable company would mount a box called a NIU or some other acronym, that would have a cable connection and a phone wire block. It would connect to the cable drop before anything else on the line and pass through signal for television or internet. This would connect to a 5ESS switch, just like the baby bells use, and was switched data, meaning
64Kbps all the time. It uses different upstream and downstream bandwidth from the Internet traffic. They were sometimes powered by the cable system, sometimes from a battery backup on site.
Now, many cable companies are moving to VoIP systems that run on the current Internet infrastructure they've built for the high speed internet. They use a special cable modem that has 2 phone jacks on the back, next to the Ethernet and USB ports:
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do share the bandwidth used in the house, usually not that much though. They also require a battery backup for lifeline service, which at some point may stop working and I'm sure will requie a technician to come out and replace.
The best thing to do is call in and ask what all is involved in an installation. In some areas I'm sure they are running both systems at the same time, with the idea of eliminating the switched service at some point, so that's yet another thing to consider.