A few months ago I purchased the same cable gateway as you did, so I will relate the general steps that I took in getting mine working.
The first thing that I did was to connect the Comcast cable to the back of the unit and then plugged in the power cord into the back of the unit and then plugged the other end of the power cord into the electrical outlet. At this point I let it sit for about a half hour so that it could be recognized by the Comcast network and whatever other software etc. that needed to be updated about it could be. I believe at the end of the waiting period all of my lights were on or flashing except for the two phone lights.
Next I plugged in the telephone to the back of my unit. I then went to the web site address outlined in the instructions and followed the prompts to actually activate the unit. I believe after this step that it was something around twenty minutes or so before all of the lights settled down to where the ones that should be constantly on were and the two wifi lights would blink. I have only one phone line and the Line1 light was steadily lit up at that time. The internet worked and the phone worked as well.
If you have done these similiar steps the the first place to look wold be is the Line1 light on the unit lit up and is the phone line plugged into the jack on the back labeled for Line1? If you have just a single phone line and the Line1 light is not lit up but the Line2 light is lit up plug the phone jack into the Line2 jack on the back of the unit and check to see if your phone is working.
If you are still having issues with the phone not working, I would suggest contacting Comcast support and asking for their assistance in reprovisioning your unit/activating the unit for internet and voice.
Hope this helps you out.