Normally they will harass you to return the old hub (gone are the old days when they didn't give hoot). If they do forget you could repurpose the hub as a wireless access point connected by ethernet, but in all honesty the Hub 3 wifi was never that great, and my personal experiments with both an old Sky hub and an old VM Superhub persuaded me that paying money for a dedicated device is better. If all you need is an access point, the Netgear WAC104 is a decent choice for forty quid. Also worth bearing in mind that a cable hub is a power hungry little beast because of the cable signal processing, and that's still whirring round even if there's no cable connection. In three years that modest extra energy use would actually offset the upfront cost of that Netgear access point.
