New iPhone 4S, activated, no service?

I got a new 4S two days ago, activated at a corporate sprint store. Everything seemed to be working fine, but when I got home my status bar would say "searching… " then "no service." Also, there's always a little circle where the 3G should be. No Internet without Wi-Fi. My iMessages send, but they don't actually get delivered until A LOT later.
I've tried rebooting, airplane mode on/off, calling ##873283#. Nothing works.

Try reset network setting

And if it still not work then you can contact them and report the issue