1. Replace void with String in class' methods

2. Classes implement interfaces
3. Add interface use demo

Callable.java

@@ -0,0 +1,3 @@
+public interface Callable{
+    void call();
+}

Emailable.java

@@ -0,0 +1,3 @@
+public interface Emailable{
+    void SendEmail(String text);
+}

Main.java

@@ -20,10 +20,20 @@ public class Main{
         ArrayList<PersonalContact> pc = new ArrayList<PersonalContact>();
         ArrayList<WorkContact> wc = new ArrayList<WorkContact>();
 
+        Callable if1 = new PersonalContact();
+        Callable if2 = new WorkContact();
+        Emailable if3 = new WorkContact();
+
         BufferedReader br = new BufferedReader(new InputStreamReader(System.in, System.console().charset()));
 
         char ch = 0;
 
+        {
+            if1.call();
+            if2.call();
+            if3.SendEmail("Example email");
+        }
+
         while(true){
             MenuPrint();
 
@@ -222,13 +232,13 @@ public class Main{
 
                     for(PersonalContact x : pc){
                         if(x.name.equals(name)){
-                            x.getInfo();
+                            System.out.println(x.getInfo());
                             break;
                         }
                     }
                     for(WorkContact x : wc){
                         if(x.name.equals(name)){
-                            x.getInfo();
+                            System.out.println(x.getInfo());
                             break;
                         }
                     }
@@ -236,22 +246,22 @@ public class Main{
                 }
                 case('5'):{                 // Show all contacts
                     for(PersonalContact x : pc){
-                        x.getInfo();
+                        System.out.println(x.getInfo());
                     }
                     for(WorkContact x : wc){
-                        x.getInfo();
+                        System.out.println(x.getInfo());
                     }
                     break;
                 }
                 case('6'):{                 // Show all work contacts
                     for(WorkContact x : wc){
-                        x.getInfo();
+                        System.out.println(x.getInfo());
                     }
                     break;
                 }
                 case('7'):{                 // Show all personal contacts
                     for(PersonalContact x : pc){
-                        x.getInfo();
+                        System.out.println(x.getInfo());
                     }
                     break;
                 }

PersonalContact.java

@@ -1,13 +1,13 @@
-public class PersonalContact extends GenericContact{
+public class PersonalContact extends GenericContact implements Callable{
     String birthdate;
     String commentary;
     String address;
 
-    void getInfo(){
-        System.out.println("\nВся известная информация о " + this.name + ":");
-        System.out.println(this.number);
-        System.out.println(this.birthdate);
-        System.out.println(this.commentary);
-        System.out.println(this.address);
+    String getInfo(){
+        return this.name + " " + this.number + " " + this.birthdate + " " + this.commentary + " " + this.address;
+    }
+
+    public void call(){
+        System.out.println("Совершён звонок!");
     }
 }

WorkContact.java

@@ -1,13 +1,16 @@
-public class WorkContact extends GenericContact{
+public class WorkContact extends GenericContact implements Callable, Emailable{
     String company;
     String duty;
     String email;
 
-    void getInfo(){
-        System.out.println("\nВся известная информация о " + this.name + ":");
-        System.out.println(this.number);
-        System.out.println(this.company);
-        System.out.println(this.duty);
-        System.out.println(this.email);
+    String getInfo(){
+        return this.name + " " + this.number + " " + this.company + " " + this.duty + " " + this.email;
+    }
+
+    public void call(){
+        System.out.println("Совершён звонок!");
+    }
+    public void SendEmail(String msg){
+        System.out.println("Письмо отправлено!");
     }
 }