You can do it two different ways:
1) Go to the website and choose Contact Us
2) Email them directly at
ecare@cc.sprintpcs.com or
ecare1@cc.sprintpcs.com or
ecare2@cc.sprintpcs.com
There may be more emails (in fact I think there's an ecare3), but they all go to the same place as far as I can tell.