Does one who swore by divorce not to speak to his wife on the phone for a month, then spoke to her on the same day, break his oath?

If by your statement: "By my oath" you intended the obligation of an expiatory offering for an oath (kaffarat yamin (definition)) should you speak to your wife before a month has passed and you break your oath, then an expiatory offering for an oath is obligatory upon you according to the majority of scholars. The Shafi'is, however, are of the view that nothing is obligatory upon you. But if you intended by it the occurrence of divorce, then nothing is obligatory upon you; because divorce does not occur except with an explicit لفظ صريح (pronouncement) or a kinayah (allusion) accompanied by intention.