I have recently started going to massage parlors and noticed that most ads seem to indicate a preference for calling ahead.  The few places I have been to seem to have only 1-2 girls working and 3-4 rooms.  Don't know if this is the norm or not.  

I'm not quite sure what you are expecting: no appointment, ring the bell and walk-in service? There is no place that I know (Boston, NYC) that will answer a buzzer or a knock without some idea of who is expected on the other side.  

It may be that the places feel it somehow protects them from LE infiltrators.  Not sure how that works, but in any case, I don't think you have much to worry about if you use a hobby phone that can't be linked to you

Most AMPs especially, are quite open to walk in traffic. I have been to dozens and dozens of MP's in several states without an appointment, I just simply walked in and rang the buzzer.  

If he was I would have deferred to your local knowledge, but contrary to what you New Yorkers believe, NYC is not the center of the universe. lol In most other parts of the country the way I described things is how they work.  

The SOP is pretty much what GaG described.  The only time I make an appointment is if I have the personal number of the masseuse.  Otherwise I just walk in and take whoever is available at the time.  Rarely do I get told to come back later.

.....and the photos of the ladies in the cheesy local rag newspapers ads are not even close to what the girls actually look like.

As for the photos, it is not clear to me:

..and AMPs are a fun diversion on occasion. Probably at the bottom of my service preferences, but they can be a great spur of the moment option.

(Who am I kidding?  I love to be nosy.)

No I've never gotten any weird vibes, but I have gotten more than a few raised eyebrows.
In a couple of places it took a few visits before anything happened, but I'm sure that happens to guys sometimes too.

there is no requirement to call though sometimes a wait is inevitable.  Phone calls are preferable...  especially if you want to request a particular gal.  I had a gal who I liked at the last place & I called & asked for her & booked an hour out.  I called from outside & she met me at the door...  but that was because I liked her.  
Another place I called ahead & was given a time something o'clock...  I passed but in actuality it was less than an hour & should have found a coffee shop to kill the required time.  
Hobby phone...  just as necessary for MPs as other services.  

I was required to fill out a form once at an AMP in LA.  Similarly, it momentarily took me by surprise, but I just entered a fictitious name, address and phone number.  Ended up going there 2 days later and went through the charade again.  If they don't check ID, what's the point in having you fill out a form?  Does anyone actually fill in real information?  If you do fill in real information do they send advertisements and coupons to your address?

so the MPs go along with it just to avoid problems.  

I'm surprised they even knew how to get another woman off.  Some don't even know how to skillfully get a man off, which is a hell of a lot easier than satisfying a woman.

I'm pretty easy to satisfy, and most of the older women seem to know what to do. Sometimes I have to guide the younger ones a bit....but they are quick learners

A lot of the AMPs in Texas have signs posted that they do NOT offer massages. Rub downs seems to be the accepted language

to require that just about any kind of physical contact between two people for pay requires some kind of certificate.  I hope judges throw out the laws for vagueness and being overly broad, but I won't hold my breath on that

To avoid practicing "Licensed Therapeutic Massage" (LTM) WITHOUT a license, they just call it "body rub.

In my state, the heat is on...  there are new laws & ordinances being enacted to regulate body rubs...   may cities have (sadly) regulated them out of existance...

Just buy a burner phone register it though a pay phone and use cash only!! problem solved.  

...I've seldom made appointments. Simply stepped inside and buzzed. A few places suggested I call ahead next time, so I did for them. But the vast majority I just walked in.