[rufius]

You can disable iMessage altogether. Sure you can't uninstall it, but you can choose to simply not have it enabled on the phone: https://support.apple.com/en-us/HT203042

Basically no user would do this but it's not somehow magically forced on the user.

[Two4]

You could also disable internet explorer - the antitrust comes in when you pre-empt any competitive consumer choice by forcibly bundling the application, iirc.

[wpm]

iMessage is an entirely separate service. It’s inactive until you activate it. It costs nothing to not enable. My dad refused to turn it on until last year but his iCloud account functioned without issue so he wasn’t “punished” or dark patterned into turning it on.

Is the Camera app an antitrust issue too? Any bundled application?

[xg15]

Not an iPhone user, but if iMessage is also the sole permitted SMS client for iOS, how would you send or receive SMS messages when iMessage is disabled?

[wpm]

iMessage is a service. Messages is the SMS app, that will send iMessages to people who have it enabled.