Houston (IAH): free WiFi, solid lounges.
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Yes. Free WiFi is unlimited across the airport.
Lounge quality here is solid. A day pass, often purchasable without status or a premium ticket, can be well worth it for a longer layover.
United Club lounges are spread throughout, alongside a smooth inter-terminal train.
It depends on how long you have — check the amenity above, and otherwise treat it as a functional connection rather than a destination in itself.