Unlocked AT&T S7 Active - moved to T-Mobile: Not working well.




    I've had a lot of problems with an unlocked AT&T "Samsung Galaxy S7 Active" trying to get it to work on T-Mobile.


    This was a phone I bought myself, and I got it unlocked myself (and had it on Cricket division of AT&T for most of a year)


    It's been quite a struggle. I've had several T-Mobile people on voice working on this.


    What is it doing now, or last time I checked?

    - Voice and text messaging frequently die. This requires me to turn Airplane mode on, and then off again. This almost always fixes this problem. Until it does it again. Needless to say, this makes the phone useless for receiving urgent phone calls and texts, because chances are the connection will have died later when one of these calls or text comes in.

    - There is NEVER any connection to LTE! The best I get is T-Mobile HSPA or AT&T roaming. Even when I verify that the T-Mobile bands are accessible, and also verify that it works great from another phone. I can't get to Band 12 even when I force the phone using *#2263# to only use LTE Band 12.

    - When roaming into AT&T, it is often "emergency calls only".



    What has been done?

    - The Samsung dial-pad radio check of *#2263* has been toggled various ways with some improvement (WDCMA only seems to help sometimes), but it is usually left at the default: automatic with everything on.

    - The proper APN, T-Mobile LTE US, has been created and destroyed and created with guidance from T-Mobile help many times.

    - This APN has been tried, as has the default T-Mobile GPRS APN.



    The T-Mobile SIM is good: I've removed it from the S7 Active and put into an unlocked T-Mobile supporting "Axon 7".


    - When in the "Axon 7", I get (relatively) blistering speeds of from 5 to 9 mbps on LTE, usually Band 12 when I check.

    - Roaming onto AT&T works better.

    - I've never had "emergency calls only" when in AT&T territory.

    - I can't recall seeing voice/text EVER die...

      All replies

      • stevetjr

        What OS is the phone on?  The issue with it just "dropping" connection even though there are bars was reported by quite a few folks on the forum here with the S7's on MM.  Nougat seemed to resolve those issues.


        As for the AT&T roaming, I have heard the same thing with Verizon phones when they are unlocked with a TMO SIM (or any carrier other than Verizon) and then try to roam back on Verizon.  From what it sounds like is some how that IMEI or some other identification is still in their system and even though it's a different SIM the system recognizes the device and doesn't see an active account and won't let it roam.  That of course is just a WAG but it's not the first time I have heard an issue with roaming issues with an unlocked phone and roaming on the previous carrier's network.


        As for Band 12, TMO's network is set up to use it only when Band 4 (Band 2 in a few markets) isn't available or is to weak to use.  TMO's bulk of spectrum is in the Band 4 or 2 area usually at least 10x10 or in a lot of major markets even 20x20.  Band 12 is at the most 5x5MHz wide channel so to keep it as free as possible for those who need it indoors or away from a tower the phone will default to Band 4 or 2.   In my neighborhood for example is in a bit of a bowl surrounded by trees and until they launched Band 12 in my market I was strictly a wi-fi caller at home, now I have Band 12 but as soon as I go up the hill to the entrance of the neighborhood it rolls right back to Band 4.


        Does the Active have an option for VoLTE?  I know AT&T said they were working on it but not sure they ever got it launched yet.  Just wondering if you try toggling that to the opposite of what it is or if it doesn't have the option maybe that is somehow disabling the LTE on TMO's network. 


        I have heard folks with Verizon phones having data/APN issues like something Verizon is hardcoding into the APN.   I know with my Samsung besides editing the default APN, I can add an alternate APN (used to and occasionally still need it when roaming in smaller countries to get around IPv6 issues), are you editing the primary or building an alternate and then making it the active APN?


        Well just spitballing a few ideas hoping something works :-)

        1 of 1 people found this helpful
          • magenta1331207

            Thanks for the comments:


            1) The S7 Active is on Nougat 7.0


            2) I am doubting there is any Band 2 or 4 in my area. Any time I have checked, the nicely working "Axon 7" on T-Mobile shows Band 12... and, checking now, it is the same. Seems to be either Band 12.... or AT&T roaming.  Or nothing. I've found some areas that are nicely covered by AT&T that won't roam at all from T-Mobile. All of the above is based on the experience of the "working nicely" Axon 7. To show what the T-Mobile situation in my area should be... what exists, and that the S7 Active can't work with.


            3) I can't find VolTE


            4) I've tried all of the above with the APN. The primary, "T-Mobile US LTE", in fact does not exist on my phone unless I create it. If I reset things, it won't get re-created and instead the default is "T-Mobile GPRS"


            (Also, what are the roaming issues with iPV6 in smaller countries? Another topic, but of interest to me since I will roam in Europe in a few weeks).

          • stevetjr

            The VoLTE might be the issue then with LTE and Band 12.  There are some phones from non mainstream manufacturers that have had to disable Band 12 to comply with TMO requirements because if it isn't certified with E911 and VoLTE they don't want to be liable if you can't call in case of an emergency because there are a few markets where they do only have Band 12 service (not even any GSM/HSPDA) so wondering if because AT&T may have disabled (or what they typically do so you don't see that you don't have it and have Samsung hide the menu in their version) VoLTE that it is messing up Band 12 which it sounds like is the only LTE service in your area.


            As for the IPv6 issue;  Some smaller countries haven't gone to IPv6 yet so while you can make calls your data won't work with the current APN so you have to change the IPv6 to IPV4 and the fast.t-mobile.com to epc.t-mobile.com, then it works.  So I have an alternate APN build just for that, but in Europe you shouldn't have an issue, at least I haven't.  Usually it is Central America or some smaller island countries that I have run into it. 

            1 of 1 people found this helpful
            • stevetjr

              LOL, Samsung of course is mainstream but there are phones like I think it is Oppo?? and I know there is a Huwia (or something like that) that claim to have Band 12 but TMO won't certify it because the mfr won't go thru the process.  In your case AT&T most likely hid the VoLTE option because they don't want you to realize that other carriers (or TMO in particular) have had it for years and since it is hidden/disabled it is causing an issue with the LTE most notably the Band 12 LTE.  If you are ever in another market would be curious if it will log onto LTE if Band 4 or 2 is available.


              As for Europe just have roaming turned on/enabled.  When you turn on you phone when you land you will probably get a welcome text message.  Just remember that most of TMO's roaming (outside of Canada and Mexico) is 2G so it can be a bit pokey but definitely better than paying for it lol.  Calls are a flat $0.20 per minute in most countries although (and doubt the Active has it) but if the Axon 7 has wi-fi calling you can call or get calls from a US number (when using Wi-Fi) calling for free.  Calling a local number on Wi-Fi is still the $0.20 per minute.   So when international and kids need to talk to us they just send a text message, we will find Wi-Fi and then call them.  Heck last time it was near lunch, they needed something and sent a text message so we stopped at the Hard Rock in Dublin and used their free wi-fi and called home for free :-)

              • gooby

                My brother had the same exact problem with his AT&T Galaxy S7. After hours and hours of scouring the internet I finally fixed the issue on his phone. I'm not especially tech savvy but was able to do all of the steps I had found to flash the phone with TMobiles software basically overwriting ATTs settings. Before doing this the calling and texting over wifi didn't work and he would frequently get NO internet even though he had full bars. My brother has an apple computer as do I and our parents only have apple computers as well. This made it 10 times harder to get the solution to work as the software used to wipe the att software off and load T-Mobiles settings instead is made for Windows computers. If you are interested in doing this I can go back and look for all of the links for you to be able to do this. Like I said, I literally spent over 20 hours total trying to get all the information and pieces to get it to work. So if I could save anyone else the same trouble I would be happy to help!!! I wish T-Mobile just had a way to do this as a service to anyone bringing their own device as this would save everyone time and frustration. 

                • automatonflux

                  I had this same problem and tried everything that's been mentioned on this thread along with many others. I found "a fix" that's worked consistently:


                  The data connection loss only seems to happen after the phone is reset (turned off and back on). To get the phone to regain data connection do the following:


                  1. Remove SIM card

                  2. Navigate to Settings > Connections > More Connection Settings > Reset Network Settings

                  3. After network settings are reset, insert SIM card


                  I tested it multiple times and I was able to get the network back every time.


                  Hope this helps!