The "o" means you are on the older 1XRTT data network. It shouldn't affect your abiltiy to make and receive calls or texts, it would just make anything that required internet access much slower.
Have you tried resetting your device by pressing and holding the Home button and power button until the silver apple appears? Also, try dialing *228 <call> and then select option 2 when asked. Let the call finish and end itself. If none of that works, try Settings>General>Reset>Reset Network Settings (note: you will have to enter WiFi passwords again). If none of those works, you might need to make an appointment at the nearest Apple Store. Verizon can also swap the phone out for you if it is under warranty and needs to be replaced but the phone will need to be shipped to you. Apple does it on site.
Best of luck.