The question came up regarding the availability of the emergency 911 functionality at the park.

here is what I found out:

from Arnie Lindauer-DNR

911 function:
You had a question as to whether or not 911 functions within the park. I am confident you will find that you can effectively contact 911 emergency services by using a cell phone in the park or by using one of the pay phones. I suggest that you ask for more detailed information at the park office when you check in.