Report #0024474 explained this issue in detail, specifically that the problem occurs when the unit has *no* radio. kbTell with DIRECT should not require a radio, that's the whole point of direct.

This command: ["090_ambient_special_00","A_hub",nil,"DIRECT",nil,nil,1] call BIS_fnc_kbTell; does not produce sound unless the speaking unit has ItemRadio linked. It has nothing to do with what channel the speaker is using. I have literally spent hours troubleshooting this. kbTell automatically switches channels based on context, so if the user is far away, then it would require a radio. At close distance it switches to DIRECT automatically. Worked perfectly in Arma 2, but in A3 it only recognizes direct mode when the speaker has a radio (which defeats the purpose of direct).

Examples where this matters: any scenario where the player is prisoner and has no items, the player will have no voice. Speaking to most civilians, they will have no voice. {F26470}