An essential element of crime in general and particularly 911 emergency call center abuse is mens rea, expressed in the particular case as absence of good faith.
Here is the first such Oregon ordinance that fell to hand.
The following persons or words used in this chapter shall be defined as set forth in this section:
[ ... ]
B. “Misuse of the 911 system” is a request for emergency response when no actual emergency exists and when the caller does not have a good faith basis to request emergency assistance. This chapter shall not be applicable to mechanical activations of request for assistance which are dealt with in Chapter 5.20 ECC, nor shall it be interpreted to impose liability on any person who makes a good faith request for emergency assistance based on a reasonable factual basis that an emergency situation exists. [Ord. 3252 § 1, 1999].