diff --git a/lesson_4/phonebook/book/book.go b/lesson_4/phonebook/book/book.go
new file mode 100644
index 0000000..277f4b9
--- /dev/null
+++ b/lesson_4/phonebook/book/book.go
@@ -0,0 +1,57 @@
+package book
+
+import (
+	"fmt"
+	"time"
+)
+
+type PhoneBook map[string]PhoneNumber
+
+type PhoneNumber struct {
+	Number        string
+	LastUpdatedAt int64
+}
+
+func (book *PhoneBook) Add(name, phoneNum string) error {
+	if _, exists := (*book)[name]; exists {
+		return fmt.Errorf("name %s already exists", name)
+	}
+
+	(*book)[name] = PhoneNumber{
+		Number:        phoneNum,
+		LastUpdatedAt: time.Now().Unix(),
+	}
+
+	return nil
+}
+
+func (book *PhoneBook) Get(name string) (PhoneNumber, error) {
+	if numberData, exists := (*book)[name]; exists {
+		return numberData, nil
+	}
+
+	return PhoneNumber{}, fmt.Errorf("no entry found for %s", name)
+}
+
+func (book *PhoneBook) Update(name, newPhoneNum string) error {
+	if _, exists := (*book)[name]; !exists {
+		return fmt.Errorf("name %s does not exist", name)
+	}
+
+	(*book)[name] = PhoneNumber{
+		Number:        newPhoneNum,
+		LastUpdatedAt: time.Now().Unix(),
+	}
+
+	return nil
+}
+
+func (book *PhoneBook) Delete(name string) error {
+	if _, exists := (*book)[name]; !exists {
+		return fmt.Errorf("name %s does not exist", name)
+	}
+
+	delete(*book, name)
+
+	return nil
+}
diff --git a/lesson_4/phonebook/go.mod b/lesson_4/phonebook/go.mod
new file mode 100644
index 0000000..000f3fe
--- /dev/null
+++ b/lesson_4/phonebook/go.mod
@@ -0,0 +1,3 @@
+module phonebook
+
+go 1.22.2
diff --git a/lesson_4/phonebook/logger/logger.go b/lesson_4/phonebook/logger/logger.go
new file mode 100644
index 0000000..b82cfbf
--- /dev/null
+++ b/lesson_4/phonebook/logger/logger.go
@@ -0,0 +1,30 @@
+package logger
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+)
+
+var (
+	warnLogger = log.New(os.Stdout, "WARN: ", log.LstdFlags)
+	infoLogger = log.New(os.Stdout, "INFO: ", log.LstdFlags)
+)
+
+func Info(message string) {
+	infoLogger.Println(message)
+}
+
+func Warn(err error, messages ...string) {
+	if err == nil {
+		return
+	}
+
+	message := "An error occurred"
+	if len(messages) > 0 {
+		message = fmt.Sprintf("%s: %s", message, strings.Join(messages, " "))
+	}
+
+	warnLogger.Printf("%s: %v", message, err)
+}
diff --git a/lesson_4/phonebook/main.go b/lesson_4/phonebook/main.go
new file mode 100644
index 0000000..57a38c8
--- /dev/null
+++ b/lesson_4/phonebook/main.go
@@ -0,0 +1,157 @@
+package main
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+	"time"
+
+	"phonebook/book"
+	"phonebook/logger"
+)
+
+func main() {
+	phoneBook := make(book.PhoneBook)
+
+	scanner := bufio.NewScanner(os.Stdin)
+	fmt.Println("Welcome to the Phonebook")
+	fmt.Println("Available commands: add, get, delete, update, list, exit")
+
+	for {
+		fmt.Print("> ")
+		if !scanner.Scan() {
+			break
+		}
+		line := scanner.Text()
+		parts := strings.SplitN(line, " ", 2)
+		command := parts[0]
+		args := parts[1:]
+		// add alice=12345
+		switch command {
+		case "add":
+			handleCommand(doAdd, args, phoneBook)
+		case "get":
+			handleCommand(doGet, args, phoneBook)
+		case "list":
+			handleCommand(doList, args, phoneBook)
+		case "update":
+			handleCommand(doUpdate, args, phoneBook)
+		case "delete":
+			handleCommand(doDelete, args, phoneBook)
+		case "exit":
+			logger.Info("exiting phonebook, bye!")
+			return
+		default:
+			logger.Warn(errors.New("unsupported command. Try 'add', 'get', 'delete', 'update', 'list', or 'exit'"))
+		}
+	}
+}
+
+func handleCommand(cmd func([]string, book.PhoneBook) error, args []string, phoneBook book.PhoneBook) {
+	if err := cmd(args, phoneBook); err != nil {
+		logger.Warn(err, "command failed")
+	}
+}
+
+func doDelete(args []string, phoneBook book.PhoneBook) error {
+	if len(args) < 1 {
+		return errors.New("missing parameters for 'delete' command. Use: delete name")
+	}
+
+	name := args[0]
+
+	err := phoneBook.Delete(name)
+	if err != nil {
+		return err
+	}
+
+	logger.Info(fmt.Sprintf("Deleted entry for %s\n", name))
+
+	return nil
+}
+
+func doUpdate(args []string, phoneBook book.PhoneBook) error {
+	if len(args) < 1 {
+		return errors.New("missing parameters for 'update' command. Use: update name=new_number")
+	}
+
+	kv := strings.SplitN(args[0], "=", 2)
+	if len(kv) != 2 {
+		return errors.New("invalid format. Use: update name=number")
+	}
+
+	name, newNumber := kv[0], kv[1]
+
+	err := phoneBook.Update(name, newNumber)
+	if err != nil {
+		return err
+	}
+
+	logger.Info(fmt.Sprintf("Updated an entry: %s -> %s\n", name, newNumber))
+
+	return nil
+}
+
+func doList(_ []string, phoneBook book.PhoneBook) error {
+	if len(phoneBook) == 0 {
+		return errors.New("phonebook is empty")
+	} else {
+		results := ""
+
+		for name, number := range phoneBook {
+			results += fmt.Sprintf("%s -> %s\n", name, number.Number)
+		}
+
+		logger.Info(results)
+	}
+
+	return nil
+}
+
+func doGet(args []string, phoneBook book.PhoneBook) error {
+	if len(args) < 1 {
+		return errors.New("missing parameters for 'get' command. Use: get name")
+	}
+
+	name := args[0]
+
+	numberData, err := phoneBook.Get(name)
+	if err != nil {
+		return err
+	}
+
+	unixUpdatedAt := time.Unix(numberData.LastUpdatedAt, 0)
+
+	logger.Info(
+		fmt.Sprintf("Number for %s is %s (last updated at %s)\n",
+			name,
+			numberData.Number,
+			unixUpdatedAt.Format("2006-01-02 15:04:05"),
+		),
+	)
+
+	return nil
+}
+
+func doAdd(args []string, phoneBook book.PhoneBook) error {
+	if len(args) < 1 {
+		return errors.New("missing parameters for 'add' command. Use: add name=number")
+	}
+
+	kv := strings.SplitN(args[0], "=", 2)
+	if len(kv) != 2 {
+		return errors.New("invalid format. Use: add name=number")
+	}
+
+	name, number := kv[0], kv[1]
+	err := phoneBook.Add(name, number)
+	if err != nil {
+		return err
+	}
+
+	logger.Info(fmt.Sprintf("Added an entry: %s -> %s\n", name, number))
+
+	return nil
+}