Found that many u2 user facing this 3g issue..In auto mode shows 3g network but while switch it to only 3g mode, the 3g network gone.This problem facing most of u2 user who chose full format+download option in sp flashtool when flashing and after fixing invalid imei they found this issue.But here is the permanent solution for it..Thnx to Santosh for sharing this method..
For fixing this issue you need-
1)Your alive Unite 2 mobile :v
2)You must be on stock kitkat firmwere
3)Recommended to follow this method on windows 7, you may face driver issue in windows8
1. Open mauimeta 3g tool (run as administrator)
2. From options select connect smartphone in meta mode
3. Press reconnect
3. Switch off your phone and connect it to usb. the phone will boot up and stuck on boot logo(dont panic its normal). After sometime in the tool u will see the phone’s parameters like gsm850,it means that it is successfully detected by the tool
5. Now select update parameter from the drop down menu,a popup will appear
6. click on change nvram database and select the given modem file
7. click on load from file and select the ini file
8. wait for sometime the barcode chec box on below will be automatically checked and will display a message load from file completed
9. now click on downlaod to flash,after sometime it will show download to flash completed. now close the popup and press disconnect.
10. Phone will turn off. then exit the software and power on the device.
ENJOY 3G FIXED 😀
Credit- Santosh (For sharing .ini files and method)