No. Sprint offers 3 days for a full refund of everything. I think they offer 14 days (30 in CA and other states that require 30 days) to return devices and cancel service, but you will be charged for what you used in those 14 days. The 72hr return is a net 0 out of pocket for you.
As to those claiming the iPhone is the only slow phone on Sprint's 3G, that is a load of garbage. It absolutely depends upon where you are.
Here is a screenshot from my Epic "4G" (no 4G in Phoenix on Sprint yet, so everyone has to use their 3G network) back in January of this year. That was typical for me around the Phoenix, Tempe, and Mesa.
I just want to further clarify if you want to cancel your contract with sprint. It is 14 days from the time of your pre-order... Spoke with the rep and they told me I have till 22nd of this month. Time to hurry!!!