Trouble with making and receiving calls in the US

[fubuki1]

I have a US talk/text/ data add-on for TWO iPhones. One of the iPhones gets very sporadic data (I turn it off and suddenly I get data for about a minute and then nothing) but I can make and receive calls. On the OTHER phone, the data seems to work but I can't receive or make calls. I can receive text messages on both phones. Any suggestions or reasons why this might be happening. This is all in San Francisco so I'd assume I have decent coverage. One is an older iPhone (7 - doesn't make calls), the other is an XS (doesn't do data stuff). 

[fubuki1]

@DennyCrane I have been on AT&T with both phones.  I never did anything on the XS (ie VoLTE). How does it explain that I can mostly get data on the 7 and NOT the XS? Just tried to change the network on the XS to T-mobile and it still seems about the same. I am somewhat worried that if I mess with both phones, I'll end up losing all abilities with both phones (ie unable to talk on XS and unable to see data on the 7) rather than fixing the issues I have... 

[DennyCrane]

@Phil_Adelphus You're right, the XR doesn't have 5G. That is odd then. You must have had data roaming on if you had data some of the time. We're you connected to T-Mobile or AT&T?

[Phil_Adelphus]

@DennyCrane   I wondered about 5G on AT&T since it is problematic, but the iPhone XS doesn't get 5G in any case so I figured the problem with that phone must be something else.

[DennyCrane]

iPhone 7 is not on PM's VoLTE whitelist, and because the US shut their 3G networks down, your only hope for phone calls is to try and find a T-Mobile 2G connection.

For data, you're likely connected to AT&T 5G, which doesn't work. Set your Preferred Network to 4G and you should be good.

[softech]

@fubuki1 

Critical part to US roaming depends on T-Mobile/AT&T coverage and whether you can connect successfully onto either network.

If the phone is not connecting to T-Mobile/AT&T, change the Network Connection from Automatic to Manual and select and test both T-Mobile and AT&T and see which one you can connect.

If your issue is with data, make sure your Roaming Mobile data is enabled and you have disabled your mobile data limiter.  Also change your network mode to 4G (and don't try 5G until you can connect and works on 4G)

If your issue is with voice, make sure VoLTE is enabled on the device setting.  And if it does not work, try to change the Network to T-Mobile ONLY, and change  Preferred Network Type or Network Mode to 2G and see if the calls go through.
Also, you can download VoIP app TextNow as a workaround to make calls and text if you have Wifi or if your roaming has data component and data  is working

[Phil_Adelphus]

@fubuki1   The 7 is unlikely to be enabled for VoLTE so for voice calls it would need to connect to T-Mobile's 2G network where available.  This is because the USA has shut down their 3G networks. 

[BKNS27]

@fubuki1 

Are both iphones have Cellular Data Roaming enabled and connected to T-Mobile or AT&T network?

Go to Settings>Cellular>Cellular Data Options>enable Cellular Data.

Then go to Network Selection and select AT&T or T-Mobile...leave on the network that has the strongest signal.