We always bring a small steamer and it works great even on jeans! Get them from Walmart or Kmart for about $21.00
I also agree with RCscoop, the cleaners onboard is very reasonable...ex, to launder and press a shirt is $2.50--less expensive then the cleaners around the corner from our home.
Also, except for a few things here and there, we never had any issues with wrinkles either and only had to break out the steamer once a cruise.
Irons onboard is not a good idea for the reasons others stated--heck, I don't even care for the ones that smoke in their rooms