Where I work the nurses are cross trained in all areas. They pick up a patient and follow the patient all the way through from admission to discharge and then pick up another. This is the best utilization of all staff....keeps everyone working and no turf battles.
RN's are generally used for acquiring PA's because they require the submission of clinical information that must be extracted from the patient's record. Many PA's can be obtained on the insurance companies website or they have a form that is fax'd back with the information that they are requesting. Just contact the particular insurance company and find out what they want and if it can be done online. When you have to do it over the phone it is more time consuming but when done online it is generally faster.