My little peanut used to have hiccupps all the time when she was just a bun in the oven. It was so funny to be sitting at my desk at work, and suddenly my stomach would be having these little 'tics' when she would start hiccuping. My OB assured me that was normal. As a newborn she continued to hiccup a lot, and again my pediatrician assured me it was normal. Even now, as a rambunctious, curious, naughty toddler, she still hiccups when she laughs too much. In this case I give her water and stop the frolickng for a few minutes until the hiccups cease. So all in all, hiccupps are normal, and decrease with age.
It's due to an immature phrenic nerve, which matures with time.