Sammy claims you can use any SIM card in the world after you've 'activated' with a SIM card from the region the device is from (in our example, Europe), but this has been proven by various (angry) Note 3 owners to not actually be the case.
The region lock is implemented in the form of a network blacklist. Beware that this is not exactly the same thing as a SIM lock, even though they are somewhat related. This blacklist blocks a number of whole countries and carriers, while a SIM lock whitelists one specific carrier. This app clears the network blacklist (region lock), but it may or may not remove the SIM lock, if present. Some have reported it works for them (for example: T-Mobile US Note3 on AT&T network: http://forum.xda-developers.com/show....php?t=2471742), but this should be considered a side-effect.
While removing the region lock does not necessarily affect the SIM lock, various users have reported that inputting a proper SIM unlock code does remove the region lock as well. You can purchase SIM unlock codes at various places on the internet for 20 bucks or so. A benefit of using such a code is that you do not need to root your device or use this app. If you are not rooting your device already for other reasons, I would personally not root it to just region unlock, and buy an unlock code instead.
- Galaxy Note 3 SM-N9005 (MI7, MJ1, MJ3 firmwares)
Right now, this has only been tested on Note 3's, and found working. Rumor has it Sammy will be bringing the region lock to a lot of devices, even backporting it to devices sold in the past (aren't there laws against this?). There's no way for me to know at this time if this specific method will keep working on the Note 3, or if it will work at all on other devices. Maybe the app will need updating, maybe Sammy will block this hack altogether, etc. Only time will tell.
In theory this hack can be done without rooting or voiding warranty with some device flashing and app modding, but I'm not currently working on that because it would be highly model-specific and I'm a root user anyway.
It is not currently known exactly when the network blacklist is updated. Beware that for example updating your firmware may cause the region lock to reactivate.
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