: Often cited as the last stable version for iOS 4.2.1.
What are you using? (iPhone 3G, iPod Touch 2G, etc.) Viber .ipa for ios 4.2.1
Since the App Store method is often hit-or-miss, you may need to install the .ipa manually. Note that this generally requires a computer. : Often cited as the last stable version for iOS 4
Repositories like the Internet Archive or legacy Apple forums often host old app libraries. Step-by-Step Installation Process iPod Touch 2G
Here is a systematic approach to finding and installing a compatible version.
Use a tool like Sideloadly or a legacy version of iFunBox .