The PA 737-200s certainly were utilised on US-based routes. As with the original (pre-National merger) PA 727-100s before them, as well as their busy German-based network, they flew on short hops from Florida domestically and to the Caribbean, and also on longer runs to Central America on "thinner routes".
My own one and only PA flight, PA300, was on a MIA
-based 737-200 (N68AF with it's "US" name "Clipper Rainbow", as opposed to its IGS name "Clipper Zehlendorf"), on Sep 27th 1989, from MIA
. It has to be said that, by then, it was a rather scruffy individual, with much-scratched window surfaces and flaking paint.
There are also shots on here of PA 737-200s at West Coast airports such as SAN
. And, of course, PA Mk2 flew several ex Carnival 737-400s.
RIP Dan-Air. Where the Secret was SERVICE.