yes and no. comcast doesn't allow customer bring-your-own cable modem for Xfi yet. So if you are renting a gateway for $10/mo, they will let you upgrade to an Xfi supported gateway at no cost.
But if you like to use your own cable modem, they don't support this. Even if you buy a modem model that is supported by comcast, they need their Xfi firmware on it.
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