I used a combination of factors that led to me getting 108 dollars off my next bill and paying only 99 for a fully eligible (150$) upgrade.
I called sprint customer service and told them i was going to cancel service and they eventually transfer you to the "retention dept"(R.D). You can also call and tell the first line customer service that you were talking to the "retention dept" and you were told to call back and ask for them and they will connect you.
The R.D. is about the only one who can make things happen that involves significant money changes. They want to keep you as a customer. I have used them in the past to get better deals on phones as well but below is what i did to get my EVO.
After reaching R.D. I was polite but told them I am sick of waiting for Sprint to drop the price on the EVO or EPIC and that even the IPHONE 4 or Droid X have been marked considerably lower (droid x has been 0$ at times). After there counters about the differences i pointed out that there is a Big difference between EVOs and the next level of phones.
Eventually the rep admitted that they couldnt change the actual price of the EVO or EPIC but they could do a 1 month of service (pre tax) off my next bill. This is the 108 dollars as mentioned. I was somewhat happy but even happier when he said just go into any store and buy the phone and that the credit is already set to be credited no matter if i buy the phone or not!
I proceeded to check RadioShacks for inventory since it was late in there 99$ trade in program around Xmas and found little luck but managed to convince the 4th Best buy i called to price match the Shacks price and got a verbal yes before driving there. Best Buy sold me the EVO at 99.99.
I thought of posting this experience when i read about some people getting a free extended battery for the EVO from Sprint Customer Service for complaining about battery life. I am willing to bet that the R.D. would be able to help EVO lovers get that extended battery for Free! Just remember when talking to most customer service they note your account so multiple attempts to regular customer service isnt always a good idea, if the first level doesn't work ask for the R.D or cancellation dept. Dont be scared when they tell you you have a contract and it will cost 105 dollars to end service, they wont let you go that easy, and you will have chances to say never-mind even if you dont get what you want