Artillery Observation planes did indeed carry wireless sets. As I understand it, they were mostly one-way sets. i.e., the airplane crew could not receive, only send. What they did, was directed the artillery by giving them the location, then when the shooting started, they would give corrections until on target, the order in a barrage.
Of course, I could be wrong, but that's how I believe it worked. If I am wrong, I'm CERTAIN someone will correct me. Just look out for the barrage!
VBR,
Al Lowe