Some time on Tuesday afternoon, about 50,000 Comcast Internet customers in Houston will become part of a massive public Wi-Fi hotspot network, a number that will swell to 150,000 by the end of June. Comcast will begin activating a feature in its Arris Touchstone Telephony Wireless Gateway Modems that sets up a public Wi-Fi hotspot alongside a residential Internet customer’s private home network. Other Comcast customers will be able to log in to the hotspots for free using a computer, smartphone or other mobile device. And once they log into one, they’ll be automatically logged in to others when their devices “see” them.