With AT&T, they actually offer HD but you must physically turn off their "Stream Saver" feature which is set to SD by default. With T-Mobile, it is necessary to enable HD pass once in their AP and you are good.
Attention T-Mobile Unlimited ONE Plan users
You are eligible for the new deal but it will not happen automatically as this is a "meet-comp" promotion. That means, if you "ask" for it, you will get it FREE. If you do not ask, your plan will remain the standard SD version without the 10GB of 4G Hotspot feature. Same with Sprint. If you are with either of these carriers, do yourself a favor and call them and ask for it. Usually you can dial 611 from your phone. Alternatively, TM's (800) number is 800-937-8997. Sprint's is (888)788-4727.
Another benefit of Verizon's new Unlimited plan is it forced TM to reduce the cost of their One Plus plan from $15 to only $5. If you do not fly often and don't need voicemail to text conversion, stay on the basic ONE plans and just ask them to add the HD and 10GB of Hotspot for FREE. Don't tell them Dr Wireless sent you though!