What to do to properly network unlock a T-Mobile Galaxy S6, other unlocking issues

Hello Android fans! Today we address some issues for some network unlocked #GalaxyS6 devices. Problems mentioned below are few and far between but they can still be doing to those experiencing them. We hope that this troubleshooting article will find be useful for them.

If you are looking for solutions to your own #Android issue, you can contact us by using the link provided at the bottom of this page.

When describing your issue, please be as detailed as possible so we can easily pinpoint a relevant solution. If you can, kindly include the exact error messages you are getting to give us an idea where to start. If you have already tried some troubleshooting steps before emailing us, make sure to mention them so we can skip them in our answers.

Below are specific topics we’re bringing for you today:

Problem 1: What to do to properly network unlock a T-Mobile Galaxy S6, can’t make or receive voice calls

So I bought a Galaxy S6 on Craigslist. It is factory T-Mobile and I am wanting to use my AT&T (Cricket) service. The phone appears to be unlocked as I can get it to show Cricket and can use text messaging, email, and Internet. Issues I am having are no calls either way and the device provides no sound (unless using a headset). In network settings I see a code of er05 invalid sim. This is apparently related to WiFi calling, which, in turn, is most likely the OS T-Mobile has installed. Could the OS also affect the sound issue? There is obviously some forms of a factory lock still as I have went to the “unlock phone” app provided by the mobile. I then requested a permanent unlock and it says the request is denied as device is ineligible. I hope this is detailed enough so far and that you can help me somehow. I have done many of the common and even advanced fixes and am having no luck. I simply need a pro!! Thank you and please help. — Terry L Smith

Solution: Hi Terry. Some phones sold as pre-owned ones sometimes have issues with them. Not everyone who sell their devices are honest enough to inform buyers of existing problems. That and with the expected possible compatibility issues are often some of the common problems unsuspecting buyers often encounter. Troubleshooting the issues you mention here depends on a number of factors and we’ll briefly discuss them individually.

Verify if phone is compatible

We would like to believe that your T-Mobile Galaxy S6 is compatible with AT&T’s network, even if your carrier is Cricket Wireless. This means that it’s physical radio can pick AT&T frequency and should allow basic network services like SMS/MMS, voice calling, and cellular data to work. Just to be on the safe side though, we strongly recommend that you verify your device’s compatibility again using Cricket’s system. To do that, follow these steps:

  1. Open Phone app.
  2. Dial *#06#.
  3. Take note of the 15-digit number, which is the IMEI (write it down if needed). If dialing *#06# won’t display the IMEI, your phone may not be compatible with Cricket.
  4. In your phone’s browser or in your computer, enter the IMEI in Cricket’s verification page.
  5. Click Check My Phone.

If Cricket says the device is compatible, that is expected.

Only unlocked smartphone may work properly

Even if your S6 is compatible with Cricket’s network, that doesn’t mean network services will work properly right after inserting your Cricket SIM card. Your phone also needs to be properly unlocked by the previous carrier. And this is where issues usually occur.

As mentioned above, not every seller tells buyers their device is not unlocked. There can reasons for that, one being the seller’s failure to contact his/her carrier before shipping out the phone to the buyer.

According to T-Mobile website, these are the requirements that must be met before a device can be unlocked:

  1. The device must be a T-Mobile device.
  2. The device must not be reported to T-Mobile as lost, stolen, or blocked.
  3. The account associated with the device must not be canceled, and be in good standing.
  4. You have requested no more than two mobile device unlock codes per line of service in the last 12 months.
  5. The device must satisfy all the Postpaid or Pay in Advance (Prepaid) Unlocking terms outlined below.
  6. T-Mobile may request proof of purchase or additional information in its discretion and certain other exceptions may apply.

If any of these conditions was not met, your phone may have remained locked to T-Mobile network, causing the problem. If you are positive though that you were able to use Cricket’s SMS and mobile data on this phone, the only reason for the current problem may be entirely device-related.

Check SIM Card Manager (If you happen to use a Dual SIM version)

Some Galaxy S6 devices are designed to be able to handle two SIM cards. If your device does not support this feature, simply skip this step.

However, if you have the S6 Duos, you should consider checking the SIM card manager to ensure that you set the correct SIM card for calls. Here’s how:

  1. Open Settings app.
  2. Tap Connections.
  3. Tap SIM card manager.
  4. Under Preferred SIM card section, make sure that you select the correct SIM card for Calls.

Clear Phone app’s cache and data

It’s possible that the issue is caused by a bug in the Phone app you’re using.  This app can be Samsung’s pre-installed app named “Phone” or any other app you may have installed. Try clearing its cache first to see if that will make a difference. If it doesn’t, do the Clear Data option.

  1. Open the Settings menu either through your notification shade (drop-down) or through the Settings app in your app drawer.
  2. Navigate down to Apps. This may be renamed to something like Applications or Application Manager in OEM skinned versions of Android 6 or 7.
  3. Once in there, look for the application and tap it.
  4. You’ll now see a list of stuff that gives you information about the app, including Storage, Permissions, Memory Use, and more. These are all clickable items. You’ll want to click on Storage.
  5. You should now clearly see the Clear Cache and Clear Data buttons for the application. Do Clear Cache first, then check how voice calling works.

Verify if speaker works or not

There are a number of things that you can do to check if the speaker works or not. The easiest is by playing videos, audio files, or listening to your recorded voice. If you feel a little technical, you can also access the phone’s service menu and check if the speaker is working or not. Here’s how:

  1. Open Phone app or dialing app.
  2. Dial “*#0*#” (without the quotes).
  3. Tap Speaker.
  4. The device should then play an audio on its own. If there’s no sound at all after tapping the box that says Speaker, the device’s speaker must be defective. In this case, you’ll need to have the phone repaired.

On the other hand, if the speaker works normally in service menu but no in normal mode, you must perform a factory reset to fix the trouble (steps provided below).

Problem 2: T-Mobile Galaxy S6 loses signal when making calls in Vodafone network

I have a Samsung Galaxy S6. I live in the Netherlands. I have no problem connecting to the wifi. I use Vodafone and there is supposed to be good reception with Vodafone where I live. I called them and they said they don’t see an issue. My phone was with T-Mobile but is not locked. I changed the network provider a few months ago after my contract ended. Usually my phone shows 3 or 2 bars but says emergency calls only. At other times it says Vodafone and shows good reception, but if I make a call, then the bars disappear and suddenly it shows no signal and can’t call. What is more surprising is that it does this quite often, even in the busiest areas where one always gets reception. Please help! — Shreya

Solution: Hi Shreya. Some specific circumstances may be different but overall, the issue appears to resemble that of Terry above so kindly refer to our suggestions for her. We will try to get an official word from T-Mobile about these issues so try to keep watch for this article for updates. There’s a chance the issue may be operating system related so there may or may not be an effective fix for it.

Make sure that you also try a factory reset as a final device troubleshooting. If that won’t work either, you can let Vodafone know so they can help you troubleshoot the problem as well.

Below are the steps on how to factory reset your device:

  1. Turn off your Samsung Galaxy S6 Edge.
  2. Press and hold the Volume Up, Home and Power keys together.
  3. When the device powers on and displays ‘Power on logo’, release all keys and the Android icon will appear on the screen.
  4. Wait until the Android Recovery Screen appears after about 30 seconds.
  5. Using the Volume Down key, highlight the option, ‘wipe data/factory reset’ and press the Power key to select it.
  6. Press the Vol Down button again until the option ‘Yes — delete all user data’ is highlighted and then press the Power key to select it.
  7. After the reset is complete, highlight ‘Reboot system now’ and hit the Power key to restart the phone.

Problem 3: Unlocked Galaxy S6 mobile data stopped working after an update

I have a Galaxy S6 from Telus Canada. I bought it factory unlocked from eBay. I only used it for only one day as it updated itself overnight and has since not been able to connect to the mobile network. I Googled the problem and ran various tests/fixes however none have worked in remedying the problem. The IMEI is good, it is running the latest android 7.0. The battery is good, the SIM card is good as i have used it in another android phone with no problems. I have downgraded the phone to 6.0.1 and gradually updated it back to 7.0. It won’t register to the network no matter what i try. — Dwightanthony

Solution: Hi Dwightanthony. Some devices can lose their unlock code after it’s been factory reset, updated, or flashed. Keep in mind that the operating system version remains even after the device has been network unlocked. If an update has been installed after it’s been unlocked, network settings may be reset, reverting them back to its original network. Depending on the device, network unlock can either be permanent or temporary. Since we don’t know much about the specifics of your device, you should contact the seller and see if they can provide the unlock code. Otherwise, you may need to find third party shops that have advanced software to perform similar network unlock procedure.


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1 thought on “What to do to properly network unlock a T-Mobile Galaxy S6, other unlocking issues”

  1. I did a factory reset on my Samsung Galaxy S6. When I restarted it, I couldn’t remember my google account. I now remember it, but it keeps telling me it does not recognize the account and that I must wait 24 hours tor try again. I have waited the time and it is still not letting me log into my google account. Do you know anything I can do?

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