Is it permissible for the husband to retract a condition upon which he made his wife's divorce contingent, and is a verbal retraction obligatory for him?

If a husband says to his wife, "If you call so-and-so, you are divorced," intending divorce thereby, then if the wife calls, one revocable divorce occurs. The husband can take his wife back as long as she is within her iddah (waiting period). The wife can then call the aforementioned person in the future without another divorce occurring, because the phrase "if you call" does not imply repetition, unlike the phrase "every time you call," which does imply repetition. Thus, once the condition (the first call) is met, the impediment is removed, and no further divorce occurs upon repeated calls.