That's pretty much what I did... I changed my account over to outlook.com at the same time, so it was worth the big pain in the arse...Another thread here:
http://forums.windowscentral.com/general-discussion/195480.htm
And a thread at MS:
hotmail suddenly stopped syncing on windows phone (without error - Microsoft Answers
I called Sprint and sounds like their solution is a hard reset. But since it seems to not be an isolated incident, I'd like to see it explained before I apply that "fix".