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[Q] How do I prevent Samsung Galaxy S 4G from connecting to AT&T?

I have Samsung Galaxy S 4G with T-Mobile in San Francisco.
Whenever I go to an area without T-Mobile signal, the phone connects to AT&T. I called T-Mobile and they said that's because T-Mobile has roaming agreement with AT&T so my phone would connect.
The problem is, when my phone connects to AT&T, I can't make any calls. It says the phone's not registered. T-mobile says that's because I'm in an area that has T-Mobile coverage.
You'd think that the phone would be smart enough to figure out that only emergency calls can be made (which is what BlackBerry does and shows SOS sign). The real problem for me is that, I have WiFi calling enabled with cellular preference, and when I'm in the basement of my office building where there is no T-Mobile signal (but there is WiFi signal), my phone thinks it has cellular signal so it doesn't activate WiFi calling, yet no phone calls are coming in b/c it's not registered to AT&T's cellular network.
Is there a way for me to force my phone to only connect to T-Mobile? I know there isn't on the regular settings menu, but perhaps experts could tell me how to do so using those star-sharp keys listed here (http://forum.xda-developers.com/showthread.php?t=842134)?
Thank you!

Set wifi preferred instead of cellular.
Sent from my SGH-T959V using XDA App

Unfortunately, that doesn't work for me because I move around a lot, and Android WiFi calling feature doesn't have handover.
There's got to be a way to prevent this phone from connecting to AT&T at a low level somehow, no?

How do I do that? Have checked the manual but can't find location where explains how to select wi-fi preferred instead of cellular. Your kind advise will be appreciated

Open WiFi Calling and select settings. You'll see Preference. Select Cellular Preferred.

I think in setting then wireless and network, then mobile networks then network operators click the default settings.... select manual and wait for the carrier to pop up.
Will this solve your problem?
Sent from my SGH-T959V using XDA App

scoop_dtx said:
I think in setting then wireless and network, then mobile networks then network operators click the default settings.... select manual and wait for the carrier to pop up.
Will this solve your problem?
Sent from my SGH-T959V using XDA App
Click to expand...
Click to collapse
yep manual is exactly what OP should do.

if the settings for network operators are set to manual then u select the network u want and it sticks unless u manually select a different network provider. u are in select automatically mode so the phone can switch all on its own. this should solve your problem as other people have already mentioned

I have tried this many times and works as long you don't turn the phone off. After I forced the phone to manually select T-Mobile I checked many times the default setting and it remained in manual until the phone was turned off. When I switched it back on it was again in automatic mode and switching to ATT when signal is low.
Is there a way to prevent this? If not, well , first thing when phone is on in the morning is to check default setting.
5/24 I finally gave up and sold the phone. Samsung says they have not received any claims regarding this issue eventhough you see it frequently in the forums. I returned back to my HTC HD2 and will wait for the G2.

[Q] Strange network connection issues

Hello fellow S3ers! I am David and I am new here.
I seem to be having a strange problem with my data network connection: My S3 is with Verizon and I have had it for several month now.
This morning everything was working fine down in FL and I hopped on a plane, set my phone to airplane mode, and returned to Philadelphia. After landing and disabling airplane mode, my phone refused to connect to any sort of data network - no 4G, 3G, or 1x. Calling and txting works fine.
I have been searching for a while now with no success. But here is the strange thing: I went into About Phone > Software Update, and clicked "Check now." Low and behold, the 4G icon flashed on and downloaded the latest update! (Which was over 140mb).
The phone updated and restarted, and now it says Software up to date. I saw the 4G icon flash on for a moment after the initial update restart, and then it flashed off. I went into software update again, and clicking Check Now caused the 4G icon to turn on again! It immediately turned off again, however. I was able to repeat this cycle several times, but now the Check now button does not turn the 4G back on at all - even for a moment as it did 10 minutes ago.
Any ideas how to solve this issue or what is going on?
Please let me know if I can provide you with any additional settings or details, but here are some details that may be relevant:
Mobile data: checked.
Network Mode: Global
APNs: None checked, EHRPD and LTE - Verison Internet are white, the rest are grayed out.
Mobile network type: LTE:14
Service State: In Service
Mobile network state: Disconnected
I appreciate your time.

I got the same issue, was working yesterday but today nothing. If I force it to cdma only I can get 3g data but it didn't stick around very long either...
Sent from my SCH-I535 using xda premium

northeast is having data connectivity issues at the moment- I called in and thats what support told me so most likely its the network right now and not your phone with the issue
http://forum.xda-developers.com/showthread.php?t=2183214

Thanks for the quick replies Neo and Chewwy.
Good news, 3G is now up on my device and it appears to be stable for the moment. No 4G yet, but I do have one more question just to make sure I didn't accidentally change something when I was troubleshooting it.
Network mode should be set to Global?
Should a specific APN be selected? Currently, both EHRPD - Verizon Internet, and LTE - Verizon Internet are white and selectable, however none seem to be checked with the little green dot. The rest are still grayed out. Is this normal, or should I select one?
Interesting to hear about the N.E. network issues. I suppose that makes me feel better lol.

Please help! No 3G or GSM, can't call, but LTE works fine.

I really need help with my device, I searched all over XDA and no-one seems to have the same issue as me.
Here is some information:
1) Nexus 6P (H1511)
2) 6.0.1 Absolute stock, no rom, no root, no custom recovery. Build number MMB29P.
Recently got a new Nexus 6P and imported to Russia. All of the major bands here are supported. And the phone worked excellent for a few weeks, but then it lost all 3G or GSM connectivity. Just randomly,didn't do anything with it, the only thing I did is move to another city but than I got back, the issue didn't resolve. LTE works perfectly but can't call or receive calls, can receive sms though. Reseting network settings and factory reset changed nothing. Tried manualy set network to WCDMA or GSM with *#*#4636#*#* command, the moment I switch to anything besides LTE the connection is lost. Contacted the provider, no problem on their side, my SIM works good in other phones, my phone with other SIMs - no.
I don't think it is a hardware issue because a few times I managed to get everything working after an hour of switching networks and bands with no particular order in the *#*#4636#*#* testing mode.
After a while I figured that if I set phone to "GSM only" on USA bands in testing mode, but at the same time set it to "LTE prefered" in the normal network settings menu. I am able to set phone to Band mode 7 and set the network back to 2G in network settings keeping it on " GSM only" the whole time and only after this compicated algorithm and after a reboot 2G and 3G starts working. But any reboot after that revertes everything back to only LTE stage. Also if I get everything working but than reset network settings everything stops working again.
I have no idea what caused such an issue, I really hope someone can help.
Sorry couldn't post screenshots because of the "10 posts rule".

Lg g4 h810 works 2G only

Hi,
I bought this phone Lg G4 h810, it shows AT&T logo whenever i boot it and the problem is despite of network mode on lte/wcdma/gsm/auto it always runs on2G internet speed and shows E sign.
I am from india and many service providers are still not offering4G internet service. But this phone doesn't even runs on wcdma. My previous phone lenovo was nicely running on wcdma and always showed the sign H.
My cellular operator is idea cellular and i had a word with them, they sent me settings and all and help me input the settings manually too, but nothing worked.
I checked even the frequencies, idea cellular is offering UMTS B1(2100) and UMTS B8(900 gsm). I checked this on LG website and these bands are compatible with the phone i bought, but still i can't get anything more than2G. Why so?
Plus there is one more problem, when i switched it on for the first time it showed update available And when i tried to update, it showed error and now always there's an icon on top left corner of phone saying couldn't install system update. I tried restarting and updating the device many times, but it's still the same.
Any help is much appreciated.
Thanks in advance.

Have you put your Company APN?

Yes i did, the company executive even helped me to manually save the settings to run the internet in a 3G mode. But all efforts in vain.

Did you solve the issue?

Anything new? I have the same problem.

I have this problem too

Try hidden menu with *#546368#*810# and under Field Test menu / Modem settings if there is VoLTE on/off chose VoLTE and restart. I have done that and my phone starts working with 4G. Don't forget to set up good APN if it's not automatically set by network provider.

scytalemk said:
Try hidden menu with *#546368#*810# and under Field Test menu / Modem settings if there is VoLTE on/off chose VoLTE and restart. I have done that and my phone starts working with 4G. Don't forget to set up good APN if it's not automatically set by network provider.
Click to expand...
Click to collapse
Hi
Under VoLTE there is another entry named "Session" and in there
RPR(on/off) switch
I enabled it and restarts but it is again on 2g
Anyone further on this issue??

I have this problem too
I was flash the stock firmware,custom firmware customizing the build.prop,changed the settings in the engineering menu *#546368#*810# disconnected volte,changed LTE bands forcibly. Nothing helps,dont work 3G LTE - 2G only(. I realized that I need to re-flash (change) the original QCN file for H810 and re-register IMEI , but I can not find QCN it freely available.

Hello there, i had the same issue. The fix that worked for me was searching for network manuallly and reconnecting again to my carriers LTE network. Worked as a charm. The issue maybe was a brutal handover as I had been travelli g from a city to another one 200 km away. So somehow I had been disconnected from the LTE network and left stranded in the 2g one. Try it it should work

Can't connect to LTE

About a month or so ago, I went on vacation to Asia with my S7. I had it on airplane mode pretty much the whole trip but turned wifi on when available.
Since coming back, my S7 stopped being able to get on to the LTE network. It stays at 4G, which is HSPA speeds on my network. There is discussion about 4G and LTE being the same, but I'm experiencing much slower speeds...5-6Mbps compared to 25-30 when my phone showed LTE.
It's definitely my phone as I put my SIM in another S7 of the same network, and that phone went to LTE. Their SIM in my phone stayed at 4G.
I've tried various APN settings, made sure GSM/HSPA/LTE was selected, reset the network settings, tried some apps that said it would force LTE...but nothing is working.
When the app does force LTE it says I am in Roaming mode. I checked the CSC and it does show my correct network carrier code.
What can I do here?

Have you manually selected and registered with your carrier's network from the network settings?
Settings > Connections > Mobile Networks > Network Operators > Search Networks
Cleared cache from recovery?
Called your carrier?
Factory reset the phone