Cell phone radiation harmful?

Does anyone has opinions or information on using the cell phone during pregnancy... Some people say that enough research hasn't been done on mother's cell phone radiations and it's possible effects on the foetal development, so it might be harmful. My friend told me not to keep my phone near my belly or not to keep it next to me at night etc. I am a bit dependent on my phone, but I try to keep it at a desk when I am not using it. Should I be concerned or be more cautious?