I have Verizon, and this symbol pops up every so often (see pic). It has happened about 3-4 time in the last 2 months. After rebooting the phone it is fine it just gets annoying. When the symbol shows up it says network not available. And suggestions.
It usually means there's a SIM card issue. The SIM might be bad, or there might be bad connection in the slot. Bring the phone to your wireless provider and see what they can do.
Them's the runtimes. You can fiddle with them in Developer Options. The G3 uses Dalvik by default. To get the Developer Options, you go to Settings, General, About Phone, Software Information, and tap Build Number seven times. I'm not saying do it, but that is how it's done.