We have Road Runner. There's no stated limit to the amount of bandwidth, when you have them as your ISP. It's not like if you have your website hosted somewhere and they measure your bandwidth.
But, I think Road Runner can tell that we have internet phone. Last year, we started having trouble with our service. We shared a "drop" from the pole by the road with our next door neighbor. Finally, the RR people came and brought a line that they said was the same thickness as the ones that run on the poles, halfway up the driveway between the two houses, and then split off 2 lines, 1 to each house. The guy said "we've amped you up and now you'll be able to rock and roll." I thought it meant that between the two houses, we were using too much bandwidth for 1 drop -- since it was 2 houses, they had to fix it, but what if our one house (with digital cable to 2 TVs, regular cable to 2 TVs, internet shared by 2 computers and internet phone) starts to use too much bandwidth? The terms of service only say that you can't connect so many devices that it starts to degrade the signal, but that number of devices or configuaration is not specified. So far, Road Runner has been good and helpful and not trying to rip us off, but I still worry.