I get this message all the time. My phone also regularly reboots and then gets stuck at the Sprint Spark bright yellow screen requiring a forced reboot by pressing Power+Volume. I've read where some people believe these two issues are connected. Hey, look- it just happened while I've been typing this- awesome! I have the Smart network switch in Advanced Wifi settings unchecked. What else can I do? This along with no data while calling is about to cause me to return the phone.
No, I haven't done that. Why would that be my first step? I'd hoped to find an answer here without having to make a special trip to a store. Doesn't Sprint have technical support other than the store?