The following article discusses the hunched forward posture we have when we are surfing on our phones.
"The average head weighs about 10 to 12 pounds. When we bend our necks forward 60 degrees, as we do to use our phones, the effective stress on our neck increases to 60 pounds — the weight of about five gallons of paint."
This posture is leading to the head forward position (that we see in some seniors) in younger people. This would cause neck and back pain, shoulder dysfunction and most likely headaches. The article also links to a decrease in mood and memory.
Anyway, since we're probably not going to stop using our mobile devices; sit up straight, take breaks and make sure you stretch into the opposite position (back and neck extension) a lot.