My son used to get them at least twice a day and sometimes as many as four times. I think it's normal, but varies by child. I actually liked it. It was a gentle reminder that he was there and doing ok. The one I'm carrying now, doesn't seem to get the hiccups, but I think she has a regular gymnastics regimin going on in there.
As always, if anything worries you consult your doctor/midwife. That's what they're there for and no one wants a worried, forgetful, hormonal woman on the loose!
-Suzy