Seen it from PC in the past. Not attributed to 2G or 3G, but specific towers with strong signal. It happens when some towers do not accept registration, but some (more distant) do. SIM gets registered (sometimes with troubles), when you dial, you are being forced to handover, but there is no throughput from these towers. I watched Cell ID's it comes to this conclusion. Solution was to position directional antenna to the working towers. Your case can differ and with a phone very little can be done.