What is Messenger for iPhone? Do I need it?

Messenger for iPhone is an iPhone app that allows you to do Instant messaging (IM) with your Facebook friends.

The current version of Messenger for iPhone is 126.0 and free:

Messenger
By Facebook Inc.

Instantly reach the people in your life—for free. Messenger is just like 
texting, but you don't have to pay for every message (it works with your data 
plan). 

Continued use of GPS running in the background can dramatically decrease 
battery life. Facebook doesn't run GPS in the background unless you give us 
permission by turning on optional features that require this.

Compatibility: 
   Compatibility: Requires iOS 8.0 or later. Compatible with iPhone, iPad, and 
   iPod touch.

Free
Category: Social Networking
Updated: Jul 13, 2017
Version: 126.0
Size: 266 MB

You definitely should use Messenger for iPhone, if you have an iPhone and your friends are using Facebook.

The picture below shows you the Messenger for iPhone in App Store:

⇒ Download and Install Messenger for iPhone

⇐ Messenger for iPhone

⇑ Messenger for iPhone

⇑⇑ Facebook - Frequently Asked Questions