Use APKPure App
Get Sonim Updater old version APK for Android
FOTA client Updater pour appareils Sonim
With this app you can update software of your Sonim phone with the official support of the manufacturer or operator.
The Android updates are so easy to install that you simply need to download a software in your Sonim phone(firmware), this app include links to download the latest android version in your Sonim smartphone.