What network are you asking about? Depends on if this is a carrier network or a WiFi network. If it is the cell carrier, has this just started with this device or is this a new device? Have you checked the coverage maps to make sure the device is used within the carriers coverage zones?
I had the Same problem with my 8320. Called up tmo, told them the problem, and they did a swap under the 1 year manufactures warentee for "faulty wireless radio". Hit up tmobile reps and let them know you need a swap.