Is it considered a sin for a person to weep and speak with the deceased when visiting graves?

Visiting graves is recommended, and there is no harm in weeping at them. Indeed, it is what a Muslim should do to remember the Hereafter and its terrors. The Prophet, peace and blessings be upon him, wept at a grave until the earth became wet, and he said, "O my brothers, prepare yourselves for the likes of this." Weeping without sound is permissible by consensus, and what is forbidden is wailing and lamenting.