Each company is affiliated with a PPO or, in some cases, an insurance company. My job is to provide acute care and preventive care. I practice the same as I have my entire career; the difference is that the preventive portion is encouraged and appreciated.
I have the option of referring within or out of network.
This is done by consultation with the patient. This part is the same as with any other practice; the difference is that I do not bill anyone and I am not controlled by an insurance company. When my friends take over for me when I go on vacation or CME they comment that "this is the way that medicine should be practiced". I agree.