So I just spoke with both a Sprint and Best Buy representative and my future advice for anyone would be to talk with the people at Best Buy from now on. I called because I too am coming from a Pre and would be 2 days short of the 1 year upgrade and I am a Premier customer. The rep from Sprint said that I wouldn't be able to take another family members' upgrade (2 year upgrade) from them to apply on my phone number and get the mail-in rebate without that phone line having the phone activated for at least 30 days with the EVO on it. That happens to be unacceptable in my opinion so I then called a rep from Best Buy and she said that is completely wrong and I would be able to take one of the upgrades (there are two 2-year upgrades in my fam) and apply it to my line and automatically get the rebate in store. I'm really glad these two companies are sharing all the rules/regulations with each other, but if Best Buy isn't supposed to be doing this, then it's probably better they aren't on the same page.
Bottom line: Sprint can't be trusted.
Hope this helps those that have upgrades within a family plan so you aren't paying full price
I don't happen to know if those that resigned a plan when they got their Pre after the 6th if they will be able to get a discount but the Best Buy rep said you can call Sprint to have them bump the date for a 1 year discount as long as it's only a few days. She said it doesn't happen all the time but sometimes they make exceptions. Good luck!