Source: Fatwa
Translated:
If the woman is in her ('Iddah) than she is still considered married, and it is ok for the man to speak to her, even about his love for her, for that might get her back with him. But if the woman is totally divorced, than the man must talk to her like he talks to any other women. And it is ok to speak about things that are necessary, like about the children for example.