Requirements:
1. rooted Mipad
2. OTG cable
3. 3G USB Modem. Probably it will work with most of them, mine is Huawei E3131
Steps:
1. install PPP Widget from play store
2. convert it to system app with Titanium Backup or any other method. Example:
https://play.google.com/store/apps/details?id=de.j4velin.systemappmover and restart the tablet.
3. place the PPP widget on the widget screen
4. click configre and put your APN , user and pass and PIN(I removed my pin from the ism card, but it should work also if tha sim card is pin locked and you put it in the settings) if provider require it.
5. Disable every setting from the configure screen. and go back to the home screen
6. Disable the WiFI
7. Connect the modem to the OTG cable, and the cable to the pad.
8. Wait around 10 seconds
9. Touch the icon of the PP Widget , your modem should appear. In a few second you will have to choose it again.
10. Press "connect" on the PPP widget. The status should get "Connected"
Now you probably dont have internet when you open the browser. that means the DNS problem exist.
Fix:
1. Disconenct the modem
2. Turn on the WifI
3. Connect to any WiFi network
4. On the Wifi Settings screen on the MiPAD pres the little arrow on the currently connected network and change the IP to Static. Most of the info should be entered automatically.
5. Delete the first DNS and enter 8.8.8.8
6. press OK on the top right
7. Disable and Enable the WiFi
Go to step 6 from the first part of the guide, follow to the end and you should have internet now.
If some smart person helps how to find a better workaround of the DNS problem please help!