What is the ruling on marriage with the intention of divorce, or continuing the marriage if reconciliation is possible, along with an agreement not to have children? And is sexual communication over the phone considered zinā (illicit sexual intercourse) or a sin? And is it permissible to marry after these transgressions?

In summary:

Your communication with this woman, involving audio and video, and what it contained of obscene language and nudity, is a great sin and a serious transgression that necessitates sincere repentance. Do not be deceived by the excuse of getting to know the reality of someone who wishes to marry her, for this is one of the weakest excuses. This act, though serious, does not reach the level of zina (fornication/adultery) that mandates the prescribed punishment (Hadd). If the woman repents from the sin she participated in, then there is no harm in you marrying her. Otherwise, it is better to stay away from her.