At my agency, the dispatch sends cars to calls based on where the complaint is. The county is divided up into 9 patrol areas. If the call is in my patrol area, I'm responding. If I'm tied up on another call, another officer may respond instead, especially if it is an emergency call or crime in progress, otherwise the call just waits for me to get to it.
Actual conversation with suspect
Suspect: Why am I under arrest?
Me: For posession of CDS.
Suspect: Man, it wasn't CDS! It was E pills!
If at first you don't succeed. . .don't try skydiving!
Note: Any laws I quote or mention pertain to the state of Maryland unless noted otherwise.