It is available in the Play Store and it is free. You will need to be rooted and you must have a USB OTG cable.
What you need ?
A rooted Android device,
PPP Widget 2
OTG USB Cable
Internet Modem with a SIM Providing internet connection
APN and other credentials provided by your ISP
1.Once you had above mention things you are ready to go, first download and install PPP Widget 2 on your rooted android device and place it on your home screen for easy access.
2.Now connect your 3 modem to phone via OTG Cable and grant root permission, in few seconds it will recognize your modem.
3.First you need to configure your modem with your APN and other credentials by tapping the configure button on the widget. Once done click on Connect and within few seconds you will be connected to internet.