To schedule and incall appt. with a known full service GFE provider, pay full GFE price and just request and receive a nude massage?
Please advise.

Is massage in your state something that requires a license? If so and if she is not licensed then yes, it is illegal though the charge may not be prostitution.

Also, if there is any sort of genital contact (yours or hers) you are more than likely violating the prostitution laws.  Heck, even what passes for a private dance in some strip clubs is, by law, an act of prostitution.

Depending on your jurisdiction, many of the elements that *surround* prostitution and enable it might be illegal.

on where you live, and how the laws read. Like BG said, it could be as simple as a licensing issue, while in other states, it could be more complicated. Try asking this on the Legal Corner. You'll find it to the left of this page.

Like they all said--it depends.  Look at your state's laws.  In some states, the law is written very broadly.  In one state, it's illegal to engage in "lewd acts" for money (or other compensation).  A "lewd act" under the law is written broadly to mean any physical contact of private parts to sexually arouse.