Facebook's move to force users to install Facebook Messenger if you wanted to chat within Facebook has met severe criticism. It turns out that people want to have all their messages right inside the default Facebook app.
Despite the criticism, Facebook wouldn't be budging (at least, not soon enough to matter). It continues to ask users to install Facebook Messenger if they want to chat or send messages. There're a couple of workarounds, though if you want to continue to chat or message from within Facebook's main app.
How to Send Facebook Messages/Chat without the iPhone Messenger App
For users who don't want to take the jailbreak-route
Step #1. Open Safari/Chrome on your iDevice.
Step #2. Go to touch.facebook.com
Step #3. You can use the message features without being prompted to download Messenger.
Step #4. Alternatively, you can also go to m.facebook.com (but note that it's an outdated interface.)
For users who have jailbroken iPhones
Step #1. Open Cydia.
Step #2. Search and install FBNoNeedMessenger.
Step #3. Restart the Facebook app.
Step #4. You should now be able to use messaging/chat without the annoying notice.
If you've got a non-jailbroken iPhone/iPad but want to jailbreak, here's how to jailbreak your iPhone/iPad using the latest tools.
Arguably, the jailbreak solution trumps the other one in terms of usability. However, I know for a fact that out of the number of users who use Facebook through their iPhone, only a handful has a jailbroken device.
For this demographic, at the moment, the touch.facebook.com website is the cleanest way to retain the Facebook experience with built-in messaging. It's not very different from the native app but it certainly is a lot slower.
FBNoNeedMessenger is a free Cydia tweak up on the BigBoss repo. It doesn't need any configurations.