I was recently given a Samsung Galaxy S2 which was locked to T-Mobile, and was asked if I could unlock it so that it could be used on any network. I naively assumed that rooting the phone would achieve this aim, but sadly this was not the case — it seems that some network providers are still sim locking phones, even on contract, and that breaking these locks still isn’t always straight-forward. With enough research however, it becomes a fairly straightforward process.
There are several unlocking methods for the Galaxy S2 which I will describe in the order I recommend trying them. Before you start you will need to have root on your phone. If you don’t have root I recommend using CF-Root or flashing a ROM that is already pre-rooted, e.g. Stock 4.1.2 ROM. You will need Odin 3 to flash either root or the pre-rooted rom. One final note of caution — this guide is written with reference to the standard international Galaxy S2 which has the code GT-I9100.
1. Once you are rooted, the first and easier method to try is to download Galaxy S2 SIM Unlock by Chainfire from the Google Play store. This is a 1-click solution which seems to have a pretty high success rate. Unfortunately it doesn’t work on all galaxy S2’s.
2. If the Chainfire app doesn’t work, then as per the advice in the chainfire details, the next thing to try is an app by “Helroz” called Galaxy_S Unlock. This also requires the installation of another app called Busybox. Install Busybox first, run it, grant superuser permissions and then restart your phone. Then try using the app by Helroz.
3. I found that neither of the first 2 apps was successful unlocking the particular phone I had been given. Fortunately there are still 3 more things to try. There is an app on the Google Play store called GalaxSim Unlock by Spocky. I don’t know if this is related to the work by Helroz (see below) or not, and I don’t know how similar it is to the app I link below for step 4. Looking at the feedback and details though, it is well worth trying!
4. When I was unlocking this phone I discovered this app before I discovered the app linked in step 3. After much reading and digging, I eventually found what is apparently an older version of the Helroz app thanks to a thread on xda-developers which is just called GalaxSim Unlock. When I ran this version and restarted the phone, all was well! This older version has now been removed from xda-developers as an updated version is on the Play Store. The old version that I used is available from our downloads page
5. If none of these apps work, you can always resort to spending some time manually tinkering — the key file is called nv_data.bin which is found in the EFS folder. You will need some kind of file explorer with root permissions — I’ve always used ES File Explorer. To find out more about how to do this and what to look for will require quite a lot of time reading — mainly on xda-developers. Use google to get you started (I haven’t provided links as the available advice and content changes all the time)