4G and iPhone XS

The message is legitimate and correct. There are four different models of the iPhone XS. None of them appear to support LTE Band 28, which according to the link you received, is required for VoLTE support. It is also a quite old model iPhone, discontinued almost 5 years ago. LTE and 5G bands change over time, as carriers purchase or abandon frequencies.

Carriers have been in the process of shutting down their 3G networks for several years. It is likely that you have been using 3G the entire time. The options that appear in Mobile Data Options are controlled by your carrier. The lack of an LTE option is a good indicator that your iPhone XS does not support the LTE bands required by your carrier.

Peter245Cie Said:

"4G and iPhone XS: [...]I also messaged telstra to check for compatibility and got the following message"

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Thank you for the screenshot.

This is a scam. See where it reads: "Please upgrade to a compatible"? A Service Provider is never going to demand that you upgrade your iPhone. You fell for it. So, secure your info.

Start with Report Items to your Carrier and Others:

You can report phone calls' and messages' info. Use my User: Using the Photos App to Report Scams - User Tip

Secure your Info:

Being ID Theft is of great concern here, then (A)verify your devices, and (B)secure your account. Open a new eMail addressee d use that for your Apple ID.

1. Verify your Devices:

Verify that all devices are logged in to your account, by using this link: Check your Apple ID Device List to See where you're Signed in - Apple Support

then...

2. Modify your Credentials:

Having been stollen, someone lily has your credentials. So, by all means, modifying them.

• Modify: your login credentials (Using Both a New eMail and a New Password for each and all sites)
• Associate: a different method of payment to your account
• Enable: Two-Factor Authentication for Apple ID and for all other accounts that have such an applicable option

Switching carriers probably will not help. New model iPhones, or any other phone, will support the newer LTE bands and probably support 5G. The cellular hardware in your quite old iPhone XS is outdated. It has been falling back to 3G because it has no 4G/LTE support in your area. It is unlikely that other carriers in your area support LTE for such an old device. The only way to know for sure is to contact them and ask if their network supports the LTE capabilities of an iPhone XS. Be sure to provide them with the exact model number as reported in Settings -> General -> About -> Model Number. Two values are available; tap the value to switch. Be sure to provide both.

BOOST Mobile does not have any of their own cellular infrastructure. They are what's known as an MVNO, or Mobile Virtual Network Operator. They use the cellular antennas and networks of established traditional carriers. In your area, that carrier is Telstra.