: Most legacy installations require a jailbroken device to use a tool called AppSync for iOS 4.0 . This allows the OS to run unsigned or older apps.
Warning: Many sites claiming to have "Facebook Messenger iOS 4.2.1 IPA" are malware traps. Avoid: app-valley, vShare, or any site requiring profile installation. facebook messenger ipa for ios 4.2.1 download
You can still send and receive basic text messages via the mobile web interface without needing a separate Messenger app. Troubleshooting Potential Issues Operating systems that support the Messenger app - Facebook : Most legacy installations require a jailbroken device