My modem and digital phone is an Arris. I think Arris has a near monopoly with Cox/TWC customers that do both Internet and Phone.
Mine's DOCSIS 2 (not 3). I pay only for 20Mbps down, 1Mbps up. That's all I really need and more.
I had a succession of Motorola (GI) cable modems without digital phone and they were OK. Went to Arris when I dumped AT&T at last (! happy face ) and went with TWC's phone/TV/Internet bundle. Not that I love TWC. But I tried 3 different classic VoIP providers - none were near enough to wireline quality to pass the WAF.
This Arris has been very good. And the phone has been as good/better than landline for quite a while. I've never purchased a cable modem; don't think I would, because TWC is on the hook to keep it working, and over the years, I've been pleased with TWC's field service.
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Arris looks similar to this:
http://www.arrisi.com/products/_images/hd/tm602.jpg
Has a built-in battery that runs it for a few hours. And it's plugged into my 1500W UPS. It and TWC's system was working in two recent local power failures. Of course, I keep a hardwired phone, and one cordless plugged into the UPS.
Info:
ARRIS DOCSIS 2.0 / PacketCable 1.0 Touchstone Telephony Modem HW_REV: 54
VENDOR: Arris Interactive, L.L.C.
BOOTR: 6.24
SW_REV: 6.1.77D.D11PLUS
MODEL: TM602G
Product Type: 00000108 010a3be2
Product Release: 00000004
Flash Part: AM29LV320MB
Download Revision: 2
Firmware Revision: 6.1.77D.D11PLUS
Serial Number: xxxxxxxx
Battery Charger FW Rev: 07.16