Does divorce occur by voice message merely upon sending it, without the wife hearing it, or is its occurrence dependent on the wife's knowledge of it?

Whoever utters explicit divorce, their divorce takes effect whether their wife is present or absent, and the husband's ignorance of this does not nullify the divorce. Explicit divorce takes effect even if the husband did not intend it, and the wife's presence is not a condition for its occurrence. It is permissible to take the wife back without her knowledge or consent if she is within her waiting period ('iddah), and this should be documented.