I don't know wheather comcast or not. I had a problem with getting dialtone. SBX could get incomming call but it couldn't get dialtone. I called tech support and they said that check the line voltage and current. I checked them. It was good. I brought new sbx(it was good at my office) and got same problem. I brought STS and Panasonic KX-T and both system has no problem with getting dialtone. I called the vertical tech support and they said to me "SBX doesn't like the someting on CO line". That was Verizon POTS line. They didn't give me the answer and they said figure it out with carrier....Do you think I can figure it out with carrier???
So what..
I collected 10 phones and SBX system from site.
I installed Panasonic KX-TA...
That's my story.