Comcast will let you do it. But they are expensive.
When I had everything with them (phone, TV, internet) it was a grand total of 100 bucks a month. The phone was sorta like cellular service: you didnt pay for long distance in the lower 48 states. 911 and the operator and everything else work normally. But if power went out you were in trouble. You had to hope the NiCad battery in the cable modem would last for a while.
JUST cable internet is 56 dollars by itself. Sort of a ripoff unless you dont watch TV at all (I dont) and have some other phone service thats a really good deal.
I have no idea what COX and MediaCom offer.
Incidentally I managed to get 9 megabit connections with Comcast while I had the whole package.
If I used Download Accelerator Plus or a file-sharing program, I could actually get data that fast.