Cross-hairs indicate a GPS-tower and router (Skyhook) based location fix. The pulsing blue dot indicates a GPS fix. GPS may not work inside, in tunnels, or other locations where the iPhone can't lock on to enough of the satellites. If it doesn't work outside in the open with a clear view of a large portion of the sky, it's possible your GPS system is not working. To get it working again, try a reset (hold Home and Sleep/Wake until you get the broken silver apple logo).
Also, in Settings > General, make sure Location Services are turned on.