Unfortunately I don't think the act as written would apply to iMessage. Seems like section 4e:
> Exemption for certain services.—The obligations under this section shall not apply to a product or service by which a large communications platform provider does not generate any income or other compensation, directly or indirectly, from collecting, using, or sharing user data.
would cut iMessage (and any other Apple service) out. I guess the argument could be made that Apple indirectly generates income from collecting data and making it available across their devices as a form of vendor lock-in, but that's shaky.
Cost of iMessage (software & service) is included in the price of iPhone/Mac. This is similar to MacOS/iOS - both are free to use but only on Apple hardware.
iMessage is end-to-end encrypted. It is unlikely that Apple collects any personal data from it -- at most, they might be collecting some aggregate data, like the frequency with which various features are used.
As far as the user is concerned, imessage does mostly operate with another "open" platform, SMS. Certain features don't work for apple users texting others, but core functionality is intact. This is also because apple innovated by creating those features while retaining SMS interoperability, and RCS didn't exist at the time.
> Exemption for certain services.—The obligations under this section shall not apply to a product or service by which a large communications platform provider does not generate any income or other compensation, directly or indirectly, from collecting, using, or sharing user data.
would cut iMessage (and any other Apple service) out. I guess the argument could be made that Apple indirectly generates income from collecting data and making it available across their devices as a form of vendor lock-in, but that's shaky.