Not supported or not allowed, which it what the AUP says?
Can you explain how using unlimited data is any different to using a phone I no longer use to permanently tether. I only need it for 1 pc. The rest of the house uses FTTC broadband but that is 20 Mbps and the Virgin is 40-60 Mbps.
FWIW many people must be like me. Rubbish broadband but a decent mobile signal. So whichever company allowed this would get a lot of business...
Meanwhile I am on a 2 year contract with Virgin at £26 per month and I can put the sim in a router. The only reason I use a router is because the best signal is in a completely different part of the house so I feed it through my lan cabling.
I really don't see why a company offering 'Unlimited Data' sims would have a problem with this