Thanks for the feedback... But I have tested both "3" and "rx" and they both work. There must be some refrence table in espBASIC that equates "rx" with "3". Mike is the one that suggested the use of rx/tx as the pin refrence.
btn = io(pi,rx)
btn = io(pi,3)
I havent tried the interrupt 'after' the "btn = io(pi,rx)" statement yet, but I will and report back my results.