Nico,

thanks.  neither =verbatim markup= (if that's the usage), nor a
non~breaking~space give me, in my output, a plain, unadorned
"xxcall_foo()".

i *do* think xxcall_foo() is very intuitive for both sets of people,
both those who want xx+results and those who want literal xxcall_foo().

so, probably there's no right, wrong.  but, imho, there should be some
fairly simple way to export, in the text one wants, a simple literal
xxcall_foo() (as well as a simple way to export xx+results).

all said and done, probably (aesthetics?) i'd go for using a hash (#) as
the "paste" character.  i guess it's a bit more complicated than just
changing:
----
: (looking-at "\\<[#]?call_\\([^ \t\n[(]+\\)[([]"))
----
in ob-element.el.  below is my cut.  (i used two invocations of
"string-prefix-p" rather than one "string-match", not being sure how
expensive the latter is compared to the former.)

cheers, Greg