Aroer - Not Aroer on the Arnon, but (if rightly written) some town in Judah, not elsewhere named.
Siphmoth, Rachal 1-Samuel 30:29, and Athach 1-Samuel 30:30, are unknown and not elsewhere mentioned; but Zabdi the Shiphmite 1-Chronicles 27:27, who was over David's wine-cellars, was evidently a native of the first-named place. It is a remarkable proof of the grateful nature of David, and of his fidelity to his early friendships, as well as a curious instance of undesigned coincidence, that we find among those employed by David in offices of trust in the height of his power so many inhabitants of those obscure places where he found friends in the days of his early difficulties. Ezri the son of Chelub, Shimei the Ramathite, and Zabdi the Shiphmite, as well as Ira and Gareb, and Ittai, and Hezrai, and many others, were probably among these friends of his youth.

In Aroer - Situated beyond Jordan, on the banks of the river Arnon, in the tribe of God.
Siphmoth - Supposed to be the same with Shepham, Numbers 34:10, on the eastern border of the promised land.
Eshtemoa - Another city in the tribe of Judah. See Joshua 15:50.

And to them which were in Aroer,.... Not Aroer in the tribe of Gad beyond Jordan, where David is never said to be, but some city of this name in the tribe of Judah; the Greek version of Joshua 15:22, instead of Adadah, has Arouel:
and to them which were in Siphmoth; which very probably was in the tribe of Judah, though nowhere else mentioned:
and to them which were in Eshtemoa; a Levitical city given to the Levites by the children of Judah, Joshua 21:14.