Keep losing 3g signal when trying to make a call

Try to backup your EFS ,and all related important data on your device,you can get a backup app for EFS on android playstore likewise the app to backup your data,i will recommend super backup, copy the backup folder on your sd card or pc ,wipe your device cache from recovery mode and reset the device after that you need to restore your EFS then restore apn setting
if the above solution does not work for your device
i wil send you a link to re write and repair the device imei.

instead of turning off the phone to reboot try a hard reset, leave the phone powered on and pull out the battery for about 10 seconds then replace the battery back into the phone and power it back up. hope this helps.

Try a firmware restore, a guide on how to do that ishere: iPhone Firmare restore. If that doesn't resolve the issue it looks like you need a new logic board which in theory you can replace yourself. Here's a guide on how to disassemble an iPhone. Maybe a tech savy friend can do it for you. If you want to have somebody else do it for you there are third party iPhone Repair Services.

Try connecting it to the computer and running an update from TomTom Home, there is a GPS fix that might help. Obviously the TomTom needs clearence to see the satalites in the sky otherwise try a hard reset with a pen in the bottom.

Do you know for sure you have good 3g coverage where you are? If so trying restoring the OS via iTunes.

try another network

just uninstall ie 8 and see if that will fix it

If you need further help, reach me via phone at https://www.6ya.com/expert/david_eb7ea98642566cc6

first, check the 3G led is on, if is on, then open the 3g connection mamager and wait about 1 minute, if doent appear signal, download the lastest drivers of 3G Modem and the updated 3g connection manager here: http://support.acer-euro.com/drivers/notebook/as_one_150.html