Originally Posted by rscarawa
Are you saying this is normal/expected behavior then?
Yes, it is but that answer still isn't right.
This phone uses battery saving techniques to power down the radio to minimal signal strength to maintain a connection.
His answer is sort of right, but not entirely accurate, and not actually in contradiction to what I said above.
Networks have a heartbeat signal that is sent periodically from the access point to the device and vice versa.
If you haven't accessed your phone, either for voice or data, for a period, it may very well be white for a moment until you perform some action to access one of those things.
The heartbeat signal is all that is necessary to maintain a "conversation" between your phone and the network, so it's not going to hit full bars unless you're actually using it. This is intentional and significantly reduces battery drain.
Usually, unless you've left your phone's voice/data functions alone for a LONG time or if you happen to be in a weak coverage area, you will have some green on your signal strength, and probably on the 3G/4G, but not full bars until you actually use one.