1)
Rashi (on Pasuk 2) writes that Moshe alone had jurisdiction over the trumpets. How will we then explain "be'Artzechem" - bearing in mind that Moshe did not enter Eretz Yisrael?
1.
Rashi (in Vayeilech Devarim, 31:28) states that Moshe's trumpets were hidden - in which case "be'Artzechem" must be referring to new trumpets that they made afterwards. 1
1
R. Bachye (in Pasuk 2): Yehoshua used Shofros and not trumpets to gather people, and David ha'Melech used a harp. See also Ba'al ha'Turim and Sifri, and Oznayim la'Torah in Psuk 2 DH ' Vehayu l'cha'.
