How to Turn your Rooted Verizon Galaxy S3 into World SIM Phone

For those of you who travel outside the U.S. often or you want to use your Verizon Galaxy S3 on AT&T or T-Mobile (For U.S. 3G/4G is not working only edge data!), here’s how to turn your rooted Verizon Galaxy S3 into a World SIM phone.
First, before we begin, you will need a rooted Verizon Galaxy S3 on stock ROM or a custom ROM that’s based on TouchWiz (such as HighOnAndroid ROM).

• Step 1. Go ahead and install the apps APN Manager, Titanium Backup, Titanium Backup PRO, and Phone info app from Play Store.  APN Manager and Titanium Backup PRO apps are pay apps but totally worth it if you want to turn your Verizon GS3 into World phone. For Titanium Backup app, you need to download both the free version and PRO key. 

•  Step 2. Next open up Titanium Backup app, hit the “Backup/Restore” tab and choose “APN Manager Pro”. 

• Step 3. Swipe to the right.

• Step 4. Choose “convert to system app”. 

•  Step 5. Next, open up APN Manager Pro app and choose “Insert APN”. 

• Step 6. Insert the APN settings for the country’s carrier you are traveling to.   Google “Carrier APN settings”, replace “Carrier” with the carrier name of the country.  For example, if you are going to use Prepaid SIM on UK’s Orange, google for “Orange APN settings”.  Then you will want to input that APN info

1.  For T-Mobile:
2.  Name: T-Mobile
3.  APN: epc.tmobile.com
4.  MMSC: http://mms.msg.eng.t-mobile.com/mms/wapenc
5.  MMS protocol: WAP 2.0
6.  MCC: 310
7.  MNC: 260

For AT&T, see here.

To get just data working, you just need to input APN, MCC, and MNC.  The rest of the settings are for getting your MMS working.

• Step 7. Once you are done inputting all the APNs for the different countries you are traveling to, you are ready.  Once you arrive at your destination, swap out the Verizon SIM card for the country’s SIM card. I am guessing you are going to be using a Prepaid SIM there. 

• Step 8. After replacing the SIM, reboot your phone and Open the Phone Info app and choose “Device info”.  Change “LTE/CDMA/EvDo” to “Global”. 

 After about a minute, you should see bars, meaning you now get voice working in the new country, congratulations, now you can make phone calls!

• Step 9. Next, to get your data working, open up the APN Manager Pro app, choose APN list, and choose the carrier of the country you set earlier.  This also might happen automatically.  If you inputted your APN right, you should be seeing Edge, 3G, or H+/4G sign on top right corner of your phone. For most of the European/Asian countries, 3G/HSPA+ is supported so they should work.  Unfortunately, only Edge will work on T-Mobile or AT&T in the U.S. as Verizon has locked out that feature. 

• Step 10. When you get back to the U.S., simply swap out your SIM card for the Verizon one, reboot.  Open the Phone Info app and choose “Device info”.  Change  ”Global” to ”LTE/CDMA/EvDo”. 

• Step 11. You should see 4G LTE working automatically but if you don’t for some reason, you can open up APN Manager Pro and choose “LTE -Verizon Internet” Manually. 

 
Yippey!  Now go enjoy your new Verizon Galaxy World Phone!
 Credits – XDA