Unlocked AT&T S10+ but can’t use Overseas SIM Card

You received an unlock code from AT&T, have you used it to unlock the phone?

Did the phone pop up a box for the code?  And once entered did it say 'unlock successful'? 

If the phone is still Network locked it should say sim not supported. There are two things to try the first thing is turn the phone off and turn it back on again and see if it connects. The other thing is to go into settings on the phone and reset the network settings. 

I've never had a phone show R for roaming. 

 And when you insert a different carriers SIM card, in that country, it's not roaming it's using local service.  It should show the new network in the upper right.

Hi, thank you for your response! 

I believe I managed the unlocking proceeds successfully. Even though there is no confirmation pop up window but there is no Locked Phone pop up notification window anymore. 

I chose the network manually to at&t and I received a text message that it says Welcome, you are roaming on AT&T. Due to network technology compatibility, traditional voice calls will not work. Please use data, SMS, app-based calling. 

Could you please guide me whether I shall keep this network to AT&T ? or better to reset the network? (and how)

I am wondering if I use AT&T network in the US, so when I travel to Indonesia, I can operate my Indonesia SIM Card in my AT&T S10+ with a local provider or not ? 

I chose the network manually to at&t and I received a text message that it says Welcome, you are roaming on AT&T. Due to network technology compatibility, traditional voice calls will not work. Please use data, SMS, app-based calling. 

This indicates you are using a foreign SIM card and an incompatible sim, and or incompatible phone on the AT&T network inside the United States.

Since you are using an unlocked AT&T phone, it is the SIM card that is the problem. The SIM card is likely not voice over LTE compatible. 

Could you please guide me whether I shall keep this network to AT&T ? or better to reset the network? (and how)

If you have the option of using a different service provider, you should change service providers. AT&T will not allow voice calls with your current service provider.  

However, if you're Indonesian service provider does not provide voice over LTE services you will get the same problem on any us Network. All US carriers have shut down their 3G service and the only Voice network available is over LTE.  

I am wondering if I use AT&T network in the US, so when I travel to Indonesia, I can operate my Indonesia SIM Card in my AT&T S10+ with a local provider or not ?

If you have successfully unlocked the AT&T S10 Plus it should work on your home network when you return to Indonesia. It will still have AT&T software on the phone and you will not receive any operating system updates.

THANK YOU Pink Panther for your comprehensive response. VERY helpful.

Currently I am using the phone only for SMS needs, no voice call. As an update that I just received many text messages from Telkomsel (Indonesia provider). SO It works fine as I need. 

I only need for voice call and data services when I am traveling to Indonesia. 

Best regards

A

Very welcome!