iPhone and United Wifi

I have had the same exact issues for the last 2 months using the same equipment and T-Mobile service. I tried a number of things based on various online forum suggestions. The only thing that solved the problem was to turn off my Norton’s 360 VPN service. My wife has the same setup minus the VPN service and has never had issues. This wasn’t a problem for a long time, so either an IOS update, App update, VPN update, or something with the United WiFi service changed. I hope this helps.

VPN frequently creates more problems than it solves. But one important fact is that when you install VPN it configures itself to the specific hardware, iOS version and network that the phone uses. If any of those change it can break the VPN. So any time you change any of these you may need to delete the VPN app and profile, restart your phone then add them back (if you still want to use VPN) so it can configure itself to the new environment.

Here's Apple's advice on VPN→

Check VPN (Virtual Private Network) and third-party software to help resolve network connectivity issues - Apple Support

Something to think about→Don't use VPN - GITHUB

There are two legitimate purposes for using VPN:

• To allow access to a private network such as a school or business when you are not on site. 
• To allow access outside of a country with a repressive government that has restricted Internet access. (This has suddenly become more important)

Any other use is risky, and can lead to problems like the one discussed in this thread. VPN disguises your location by making you appear to be somewhere else in the world. But you usually can’t control that “somewhere else”, and if it is in a location that an app isn’t approved for the app won’t work. Plus the fact that the provider of the VPN knows everything about you and your location, as well as what sites you access through the VPN. So you are totally dependent on the VPN provider’s honesty. As a start, if the VPN is free, DON’T USE IT. The provider has to make money somehow, and if you aren’t paying them then they are selling your private data to make money. But even those that charge can’t necessarily be trusted. For example, a few years ago Avast was caught selling user browsing data. They claim they have stopped doing so. 

You don’t really need VPN when using public Wi-Fi, because all communications between your device and the servers it accesses are end-to-end encrypted.

If you want VPN for privacy about the sites you visit, that’s not a good choice as discussed; instead you should download and use the TOR browser.

The other use for VPN is to “steal” content that is not available in your area. I leave this question to your personal ethics.

If you are experiencing any difficulty with third-party apps or a specific website then please contact the app developer or site publisher/host directly. Here is how

• To contact an App developer --> How to contact an app developer - Apple Support
• To contact a web publisher —> Scroll Down to the bottom of the web page. You will find: Contact Us, Help Center, Support, Terms of use etc.

For iPhone to iPhone activate iMessage and is free, no charges between Apple Devices.

With iMessage apps, you can collaborate with others in a conversation, decorate messages with stickers, share a song, and more 

Use iMessage apps on your iPhone and iPad

To activate iMessage and FaceTime using your Phone number

First, check to know whether you have an SMS plan enabled at least for One SMS*** with your carrier. Contact your Carrier (Cellular Service Provider) the agency that issued the SIM to you

If your iPhone is used with a carrier not found in the wireless carrier articles, make sure you can send and receive international SMS. (One SMS*** Only)

If you can't turn on or sign in to iMessage or FaceTime - Apple ...

*** You may not have an SMS plan enabled by your carrier for the SIM/eSIM that you use on your device. Apple Inc does not provide SMS services.

iMessages are texts, photos, or videos that you send to another iPhone, iPad, iPod touch, or Mac over Wi-Fi or cellular-data networks.

What is the difference between iMessage and SMS/MMS?