Is divorce via phone and paper considered a legitimate divorce, and is it permissible to marry now, or does it require going to court?

A divorce issued by the husband over the phone or in writing is considered valid if the husband acknowledges it or if two just witnesses testify to it. Marriage is permissible after the waiting period (iddah) concludes. However, if the wife has no proof of divorce other than a mere claim, it is not permissible to act upon it, and the matter must be referred to the Sharia courts.