The Military uses of the Palantiri.

[Inziladun]

Originally Posted by Legate of Amon Lanc

That's true, however still I believe that except for really urgent cases, one would still use the good old-fashioned way. "Hello my dear cousin, I hope everything's going fine in your land, we have produced five hundred tons of grain this year" is not necessary to transmit via the Palantír, and as it's been pointed out, the strain of using it, even by a king who had the right to it, would not be worth it in such simple cases.

I would think the Palantíri would have been certainly much used even in matters of routine discussion between Gondor and Arnor, considering the great distance seperating the two kingdoms.
The 'strain' of using the Stones was much greater when one used them as viewing devices. In mere comunication between two Stone, especially when both were in 'accord', I think the tax on the surveyors' minds would have been less.