The same thing happened to me 31 days into using a new 6700. Sprint kindly told me that since I have insurance I could just replace it. This was not an option for me at that time. The principle of it was that I had only had this phone for 31 days and there was no way in heaven or hell I was reaching into my pocket that soon to pay for a replacement. Had this happened with 6-7 months of usage, then I'd have paid.
I went to several Sprint stores to have *cough* techs look at it, and thats exactly what I think each of them did - look at it!
11 frustrating phone calls later, I was finally able to get them to send me another one; without it costing me anything but my time.
Since then they have disconnected my service 2x's stating that they havent rec'd the broken 6700.
Imagine that.
UPS tracking is my friend!
Hopefully the 6800 wont be plagued with the same dreaded headset jack issues.