I owned a towing company and was contracted with AAA..... I can tell you how it works from the towers side of the fence and what to expect when you call AAA.
A towing company that wants to do AAA work contacts AAA and says "hi, my towing company wants to contract with AAA". The regional rep from AAA comes to your towing business and "interviews" your company. They look over your equipment, give you the rundown on what AAA expects as far as services offered, time lines, etc. If you make the cut (equipment is in good shape, record keeping is done correctly, you have uniforms, everything is legit, etc) you then sign a contract with AAA to provide towing and roadside assistance for them. AAA gives you decals for your trucks and puts you into their "provider database".
Now, when Joe Schmoe is driving along and breaks down.... he calls AAA and tells them he needs help. AAA takes his information (member number, vehicle type, problem, intended destination with the care, etc) and puts Mr Schmoe on hold. AAA looks in their database and based on the location of the break down, they pull up a list of the closest AAA providers in that area. AAA calls provider 1 on that list and offers them the job, if they are busy or can't do the job for whatever reason AAA calls provider 2 on the list. Once a provider says yes I'll take it, the information on the call is given to the provider and the provider gives AAA an ETA of when they expect to arrive at the breakdown location. AAA gets back on the phone with Mr Schmoe and says we've got someone coming to help you and they will be there in about XX minutes.
Overall AAA service is worth having.....There are other "motor clubs" that offer the same thing that AAA does like Road America, Agero, and several others. I would definitely get the "Plus" membership as it tows you up to 100 miles for free. The basic membership only tows your car 3 miles for free, the idea is to get it off the road and into safety in a parking lot. Every mile after 100, or 3 depending on which package you get, is paid for directly to the towing company out of the customers pocket. The price of those miles is dictated between AAA and the towing company and varies depending on what part of the country you're in. Using AAA one time can save you enough money to pay for a couple years worth of membership.