Had to share my story, cuz I never really asked for this before. I called Business customer service (since I get discount for my bill because of the corp. I work at) and got connected to billing. I asked them if I could get the "loyalty" credit, since my contract is ending and I was planning on extending for 2 years due to my getting the EVO in June. They said no problem and I got $70 per line (3 lines total)! LOL...That covers my $10 per month EVO fee for 21 months (well, 7 months if I upgrade the other 2 lines with EVO's also), but who knows if I'll even keep the EVO after 1 year. Before she completed that, I asked her very specifically, "Would you please make sure that this won't affect my ability to upgrade my phone?" Her answer was, "No, it will not have any effect on your phone upgrade eligibility."
That was so unexpected, but SO glad some people mentioned it on here! I also inquired about waiving the $10 fee, if 4G isn't available to me by the time of launch and she seemed to think there'd be no problem with that and that Sprint might be able to work something out.