Take this for what you will, I asked two reps and here's what's one said:
03/26/2010 04:01:12PM william: "hi, i was wondering, do you have any knowledge of the release date of the evo 4g and its cost, and if 4g will cost extra? thank you"
03/26/2010 04:01:51PM Agent (Michael CC): "That is a great question, I would be happy to research that information for you."
03/26/2010 04:05:29PM System: "I appreciate your continued patience. I am still researching this issue for you."
03/26/2010 04:06:55PM Agent (Michael CC): "According to my resources, the release date of the HTC Evo 4g will be Summer of 2010. There is not a specific date available as of yet."
03/26/2010 04:09:57PM Agent (Michael CC): "Regarding cost, the service will be the same cost as with 4G devices."
03/26/2010 04:10:12PM william: "so, $70/month for everything 450?"
03/26/2010 04:12:08PM Agent (Michael CC): "Yes, that is correct."
so no info on phone price, but it looks like we won't be paying a premium for 4g, which is awesome. I'm sure they'll charge something for the hotspot app though