: iOS 4.2.1 does not allow side-loading apps by default. You will likely need to jailbreak your device and install AppSync Unified from Cydia to allow unsigned IPA files to run. The IPA File
: iOS 4.2.1 devices (iPhone 3G, original iPad) cannot run modern secure HTTPS stacks required by Facebook. Even if you installed Messenger, login would fail. facebook messenger ipa for ios 4.2.1 download
Use a tool like iFunBox on a PC to drag and drop the .ipa file into the "User Applications" directory of your device. : iOS 4
: You must find an archived version of Facebook Messenger (look for version Even if you installed Messenger, login would fail
Since iOS 4.2.1 is older than the minimum requirement for even early Messenger versions, it was never natively supported on this firmware. How to Get Messenger on iOS 4.2.1
Downloading and installing Facebook Messenger on iOS 4.2.1 is technically possible but highly impractical because official support has ended