My Mobile Data setting does not have Roaming Off button on my iPhone 16 Pro (My Carrier in Australia is Optus)

On an iPhone, many features under Mobile Services—such as Personal Hotspot, Roaming, Mobile Data, and Wi-Fi Calling—are managed and enabled by your cellular service provider. If any of these options are missing, grayed out, or not functioning correctly, it’s often due to your carrier’s configuration or restrictions.

In such cases, it’s recommended to:

1. Contact your carrier to confirm that your plan supports the feature and that it's enabled on their end.
2. Check for a Carrier Settings Update by going to Settings > General > About. If an update is available, you'll be prompted to install it. These updates can enable new features, improve connectivity, or fix issues related to your network.

Always ensure your device has the latest iOS version as well, since some carrier features depend on system-level support.

Talk to your carrier. The features you’re asking about are enabled by your carrier. Carriers also control the updates of the cellular software on your iPhone and you might have missed a recent software update.

1. Is this your corporate/organisation/enterprise/School Management iPhone? Then please contact the system administrator of your corporate//organisation/enterprise/School Management
2. If it is your device, in that case, do you have any profile installed by your corporate/organisation/enterprise/School Management?
   1. Erase the profile added by you If you have installed a profile on your own --> Install or remove configuration profiles on iPhone - Apple ...
   2. Or please contact the system administrator of the organisation who provided the profile to you

A corporate profile installed on your iPhone could potentially be contributing to the inaccessibility of certain features. 

Here's why:

• Restrictions: Corporate profiles can have restrictions placed on apps and functionalities. These restrictions might be limiting some activity, causing it to be unresponsive or quit.
• Managed Apps: IT departments might deploy specific navigation apps through the profile, potentially blocking certain functions or features.
• Security Settings: Corporate profiles often have stricter security settings that could affect app or function behavior. This might be causing unexpected behavior of an App or functions.

Here's what you can do:

• Check with IT: The best course of action is to contact your IT department. They can explain the restrictions set by the corporate profile and see what is affected. They might be able to adjust settings or suggest alternative apps or features approved for corporate use.
• Look for App Conflicts: See if your IT department uses a different app through the corporate profile. Conflicting apps might cause crashes.

Additional points to consider:

• Even if the profile isn't directly affecting the function, it's still a good idea to check with IT. They might be aware of similar issues and have workarounds.
• While troubleshooting, make sure you prioritize safety. Don't fiddle with your phone. 

By working with IT and considering these possibilities, you can hopefully identify if the corporate profile is the culprit and find a solution that allows you to use the iPhone to your liking.