...after leaving an AMP.  Asked me for license, questioned about the place which he says was under investigation.  Did anything "extra" happen (no), how much did I pay for how long, did I tip if so how much, what does the girl look like, did i take a shower, had i been there before, any medical conditions, etc.  i answered the questions and admitted no wrongdoing.

Gave me back my license.  Said I might be called in to testify.  Any validity to this?  Did i misstep by answering those questions?  I drove away, not arrested, no ticket but worried about receiving a visit at home, or something in my mailbox down the road.

Well, let's think about why folks are called to testify.  It's usually done to establish proof of some event.  In criminal cases, it's to prove that a crime took place and who did it.  So, in your example, the answers you gave don't point to any criminal event.  So what's the point of any testimony you might give?

Unless they were intending to trick you into telling a lie under oath, there is no purpose for your testimony.  The cop wouldn't have knowledge of this, so I think it was just a fishing expedition and when you didn't bite, he took a parting shot at giving you a wake up call.

because by answering any question other than your name and address (and showing your license) you have opened up serious potential problems, not the least of which is a charge of lying to police and obstruction of justice; and you can face those charges even if all you did was get a massage (wink, wink) and nothing more.  Those are very serious felonies, by the way.  They are what trip up a lot of famous people,  Martha Stewart, for example.

This is because they might get the gal to toss you under the bus and then get you to cooperate against others.

This is how modern police work is done.

But you have a strong defense that you did not use, and that defense is the Fifth Amendment to the Constitution which gives you the right to shut the fuck up.

Simply say to the officer that you do not wish to answer any of his (or her) questions beyond establishing your identity.  Then ask if you are free to go.

Next time, that is the way to go.

(still not a lawyer)

see this video and this will give you a good idea as to what to do

http://video.google.com/videoplay?docid=-4097602514885833865&ei=U4JcS9y7N46-rALjtdmeCg&q=don%27t+talk+to+the+police&client=safari#

For Jebus sake, don't do this!  You now have homework, dcbar10der, and it's to watch this video linked below.