If his kid is in the care of the state they should be helping with all of this. They can refer him to housing assistance and community resources, including paying for a phone and minutes. If he is an addict they can also refer him to inpatient treatment where he could eventually have his son with him. If he doesn't know who his caseworker is, he needs to attempt to reach out. If he knows the county his son was in while taken into care he should reach out to that agency and they should be able to connect him to the correct person.