I recently purchased an Ulefone U007 Pro (in Serbia branded as the TESLA Smartphone 3.2 Lite), which is a pretty nice and very very cheap Android phone that has a 5 inch screen, a quad-core 64bit Mediatek MTK6735M/MT6735M chipset inside with the Mali-720MP graphics and is powered by Android 6.0.
By default it comes bloated with a bunch of Serbian-specific apps that I don't use, as well as some spyware made by Mediatek themselves, which sends private information to a server in China over HTTPS.
To fix this, I thought "Hey, why don't I put CyanogenMod on there?". Stupid idea. After hours and hours of nudging things just the right way, I got my phone to boot properly, but it first showed Invalid Baseband version error and would crash when you insert a SIM card.
I realized that my OS build was bad, and I was in a hurry to get to sleep (it was 4am), I flashed the default TESLA firmware, which made things even worse and made the phone unbootable. I went to some chinese site and found a link to needrom.com with a Ulefone U007 Pro stock ROM (without Serbian apps and pretty stock but with some spyware included :/). I flashed it, I'm not going to go into details here how, and it worked, it booted, but the SIM card didn't work and the Out-Of-Box experience crashed when it tried to Activate Cellular Service. In the top left corner it misteriously said "Invalid IMEI".
After some googling and re-flashing the firmware, formatting, and flashing, I managed to get it to go past the OOBE screen and to let me dial. I dialed *#06# and saw an empty screen. What a shock, I started sweating and worrying I'd have to throw away a phone I just got because of my stupidity...
BUT... Don't fear, if this has happened to you. I have a solution to writing an IMEI to newer Mediatek chipsets, like 6735M.
Step 0: WARNING
The steps below have only been tested with the TESLA SP3.2 Lite / Ulefone U007 Pro. Trying anything posted here is at your own risk. I (Milan Kragujević) am not responsible for any possible damage to your property including your phone, your computer, your cat, etc.
If you're using this with another phone you need to obtain the AP and DB files yourself, DO NOT UNDER ANY CIRCUMSTANCES USE THE FILES I PROVIDED FOR ANY OTHER MODEL OF PHONE, YOU WILL DESTROY YOUR MODEM AND RUIN THE BASEBAND FIRMWARE!!!
Step 1: Obtaining the firmware
First, obtain the modem firmware file, available here.
If linking to this tutorial, do not hotlink the file, but instead link this page.
Step 2: Turn off your phone
Make sure your phone is turned off. For Ulefone / TESLA, unplug the USB and hold the power button for at least 20 seconds, or until the phone vibrates. If you get prompted by Android, ignore it, and force the phone to turn off itself.
Step 3: Extract the SN Write Tool and the firmware
After downloading the RAR archive, extract it somewhere on your desktop. Make sure that the full path is less than 200 characters, because if the path is too long the tool won't run.
Step 4: Run SN Write Tool
Right click on the SN Writer.exe and Run as Administrator. In the popup answer Yes.
Step 5: Configure the tool
When launching the tool, a following screen will appear:
Select USB VCOM and Smartphone with C2K.
Then click System Config and fill in everything according to the picture below:
Click on MD1DB, and select the "BPLGUInfoCustomAppSrcPMT6735S00MOLYLR9W1444MDLWTGMPV79P31lwgn" File.
Click on APDB, and select the "APDBMT6735S01alps-mp-m0.mp1_W16.18" File.
If your phone doesn't have two SIM cards, deselect Dual IMEI, otherwise select it (as is the case with the phone I have).
Step 6: Entering the IMEI
Changing the IMEI of a phone is illegal, so ONLY ENTER THE ACTUAL IMEI OF YOUR DEVICE FOUND BEHIND THE BACK COVER!!! I TAKE NO RESPONSIBILITY IN WHAT YOU DO TO YOUR DEVICE, THIS GUIDE IS ONLY INFORMATIVE!!!
In the screen above, enter the IMEI1 and IMEI2, and leave everything else to default.
Step 6: Flashing
Click OK, and quickly connect your phone via USB.
Make sure that the phone is off when connecting it.
Step 7: Success
If all went well, you should see this message:
If an error occurred, please try again, and if it still doesn't work, contact the manufacturer for help.