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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...
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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.

Network with 3G connectivity

Hello guys, i am from India. Here, I have activated airtel 3g and i am from Maharashtra state. Here, airtel network uses IDEA network for 3g packs as they don't own the spectrum. I kept my cell in 3g mode and "automatically select network", but it stays in 2g(Same doesnt happen in my note 2, using 3g in auto mode). If i manually select IDEA from the list of networks, it goes to 3g. I want to keep it on auto, like switch to 2g when 3g is not available. Settings are same. How to make it switch to 3g automatically. Preferred mode is 3g. Any problem in my handset?
Thanks

[Completed] Troubleshoot

I have got a Samsung Galxy S3 Neo(GT 19301I) from Dubai as a gift and since I am a residential of India,I couldn't access the network because of country lock.I took it to a Samsung Service Centre,they said though it is not done genuinely by their engineers,but he could individually give a try wih his souces to unlock the country lock.It also got unlocked(rooted) but a problem still persisted.I got a sim into it and accessed the network.There was no problem in the connection.I accessed the internet and there was the main problem.My network mode was set to GSM/WCDMA, so I got a internet connection of edge.The arrows of internet had some problem.So I gave a try to switch my network mode to WCDMA only and got a HSPA connection.My internet had worked great on HSPA connection.Now there is a problem with the 3G connection in my area so my network does not provide me any connection on WCDMA mode and so I had to move to Auto mode.Now the problem is that I cannot access interent with EDGE mode.The arrows get highlighted but I don't get any service in surfing or chatting.I am not able to understand whats the problem with my EDGE mode???It doesn't give me any internet outgoing and incoming.

Hi, thank you for using XDA Assist. I'd try asking for help in your device specific forum here, http://forum.xda-developers.com/galaxy-s3-neo. Check your apn and make sure it's soup for your carrier.

Thread closed.

Galaxy S6 Duos Network Issue

I need to solve an issue pertaining to my Galaxy s6 duos. The problem is that sometimes my phone's sim 2 wont work, although it is registered on the network but it won't make a call or send a message neither would it receive a call or message. After i put the phone in airplane mode and switch it back online,then the sim2 starts working. Please help me in solving this issue. What could be causing this problem?

Hmmm set sim 2 only to 2G network and check if it losse connection... (I suspect when phone leaves a 4g area and it has to connect to 3g sometimes stuck at searching ...)

I have an issue that whenever i use mobile data on sim 2 it connects to 2g. I need all the time to go and change from 3g/2g to only 3g then back again to get 3g working. Also noticed that if 3g is not in range it switches to 2g but when its in range it does not automatically take 3g.

[S6 Dual-sim] Mobile network suddenly restarts

Need help guys. Hopefully this is okay since I'm using the S6 regular Dual-sim Philippines model. I'm using 2 sims (Globe and Sun network) and I always use my Globe network for mobile internet since it's faster. Now, when I use the LTE capable network for mobile internet for a couple of minutes (possibly hours as well), both of my sim cards would suddenly shut down (their mobile icon turns hollow, mobile internet disconnects. Sorry I can't provide the screenshot since i forgot while making this post). After a while, both networks will have their signal back and I can resume browsing again. This usually becomes a problem when i play online games since the game constantly checks for a working internet connection and it cuts me off the server if i'd lose my internet for a few seconds. What i've tried is that I'd turn off the other sim card (Sun sim card) but since I also use this sim for communicating with people, I can't turn the sim off permanently. Can someone please enlighten me on what to do or what might be the problem? Is this supposed to happen to the dual-sim variant of the S6? Hope you can help me out guys.. Sorry for the long post though.
TLDR: Using dual-sim variant of S6 (Philippines). Using two sim card networks (one for internet, one for texting/calling). When using mobile internet (LTE mode) for a couple of minutes or hours, both sim networks would suddenly shut down and I would lose my internet connection. Turning the non-internet network/sim off somehow fixes the issue but I need both networks on since people would call me at the non-internet network sometimes. Is this expected from a dual-sim variant or is there anything i could do to fix this. Thanks guys!

Is VoLTE activated?