@Entity
public class Cellphone(){

    @Id @GeneratedValue;
    private Long id;

    private String number;

    @OneToMany(mappedBy="cellphone", cascade = CascadeType.ALL)
    @JoinColumn(name="id_cellphone")
    private List<Calls> listCalls = new ArrayList<Calls>();
}

@Entity
public class Calls(){

    @Id @GeneratedValue
    private Long id;

    @Temporal
    private Date date;
    private Integer time;

    @ManyToOne
    private Cellphone cellphone;
}