I'm pretty sure this information is incorrect.
Section 230 of the Communications Decency Act is what gives "interactive computer service" providers immunity from the content of posts made by their users. If you're thinking of some other law, then please specify exactly what it is.
Section 230 is fairly brief, and quite clearly written.
https://www.law.cornell.edu/uscode/text/47/230
Subsection (c)(1) makes it clear that an "interactive computer service" provider (or user) is not a publisher. (c)(2) says that restricting access or availability of information (i.e. limiting what appears on the service) cannot result in civil liability. (d) says what the obligations are.
There are more provisions, which can be read at the above link.
The definitions used in Section 230 are listed under (f). The distinction between "information content provider" and "interactive service provider" is an important one, when it comes to who is responsible for what under the law.
I don't see "platform" defined in (f), so unless you're using it as a synonym for a defined term in the legislation, you'll have to explain what you mean by "platform", using the definitions that
are used.
Telephone lines are covered by different statutes. One of the main distinctions is point-to-point (telephone) vs. general access (interactive service provider).