Yeah, I would contact the carrier, or just use good duo depending on what operating system your friends are using of this Android you should be fine using Google duo if it's IOS you wouldn't be able to.
You can use Duo on the iPhone to video chat with Android users who use Duo. I do. A lot of friends eith iPhones use Duo to talk to their friends on Android. Maybe do a search on youtube.
You're misleading people with that statement.
In order to access video calling and advanced messaging (RCS) on an unlocked model you'd need to use tmo's software. This issue isn't S10 exclusive however, it extends to other phones not sold directly by the carrier.
I used an unlocked S10 and Note 8 on T-Mobile, neither could access video calling. The software lacks them, simple as that. With unlocked you get all TMO bands, VoLTE, wifi calling, SMS/MMS, and carrier aggregation. Also unlocked models have a Hiya filter in dialer settings.
If video calling is important to you try Discord, Skype, Snapchat, or any app with this function. Alternatively stick to T-Mobile variants in the future. Edited for clarification.
Sadly true. I noticed my video call function disappear when I went to the unlocked model over the Verizon branded S10+. But the other options that opened up were well worth it.
Skype has always been good to me though