Section 230 provides a useful shield for retweeting and for reposting. I am not sure that long-term custody or quasi-bailment of a file for multiple users or re-users defeats common carriage status. Common carriage (the public calling of transport) is often combined with warehousing.

Back to the Future II provides a scene of long-term custody of a message by Western Union, which was in 1989 still a common carrier of messages/despatches.

Carrier would imply they only temporarily hold the files until delivery is possible and completed.. 230 is stronger in this case. E2EE content distribution networks like Signal Messenger can have carrier protections since they delete all the files after delivery or a certain amount of time

Neither side appears to have treated iCloud as a common carrier, and the court did not analyze common-carrier law.

The plaintiffs characterized iCloud as a defectively designed data-storage and sharing product. Apple characterized itself as the provider of an “interactive computer service” protected by § 230. The court adopted the latter statutory framework and called Apple a “publisher” in the specialized § 230 sense: iCloud enables users to store and share third-party content. The opinion contains no reference to “common carrier” or “carrier.”

While O’Brien v. Western Union, 113 F.2d 539 (1st Cir. 1940), involved a defamatory, not obscene, telegram, this First Circuit is relevant.

Western Union was concededly a federally regulated common carrier. The First Circuit held that its privilege against defamation liability had to be broad enough to permit rapid, nondiscriminatory message carriage. The carrier could not realistically investigate every message, and § 202(a) of the Communications Act subjected it to nondiscrimination duties.

Thus, O’Brien supports this proposition:

A message carrier ordinarily is not civilly liable to the person defamed merely because it mechanically transmitted a customer’s defamatory message.

That resembles the result in Amy, but the legal route is different:
https://uploads.disquscdn.com/images/37e69460e29a520ea6fcebce86930135bcb5c3e7a64e5799f40c0c513edfcff2.png Obscene or unlawful messages

A common carrier’s nondiscrimination duty does not normally require it to carry material whose transmission is itself unlawful. A carrier may refuse obscene, threatening, fraudulent, or otherwise prohibited communications without thereby ceasing to be a common carrier. But that does not necessarily imply that the carrier becomes liable whenever it unknowingly carries such material.

Those are two distinct propositions:

1. No obligation to carry: the carrier is legally permitted, or sometimes required, to reject unlawful content.
2. No liability for carriage without knowledge: the carrier is ordinarily not treated as the author or publisher merely because its facilities transmitted the customer’s message.

That is the relevant implication of O’Brien. The freedom to reject facially unlawful material is compatible with a broad immunity for automatic carriage of material the carrier has not identified as unlawful.

How a common-carrier analysis might have changed the framing

Had iCloud been treated as a common carrier of messages or files, Apple might have made an argument resembling O’Brien:

Apple carries or stores user communications mechanically and cannot be liable to third persons for their content unless Apple had sufficiently specific knowledge, actively participated, or violated an independent statutory duty.

That reasoning could support Apple even without § 230. Indeed, the common-carrier theory might provide a cleaner conceptual account than the court’s use of “publisher.” A traditional message carrier is ordinarily distinguished from a publisher precisely because it does not select, edit, endorse, or exercise editorial control over individual messages.

The Ninth Circuit’s § 230 terminology produces something of a doctrinal paradox:

1. Apple says it does not inspect or exercise editorial judgment over private iCloud files.
2. Yet § 230 doctrine calls the facilitation of those files a “publisher” function.
3. Traditional common-carrier doctrine would more naturally call that carriage, not publication.

The court stated that iCloud was functioning as a publisher because it allowed users to share their own content and that deciding whether to deploy scanning technology was a content-moderation decision. That is “publisher” as a statutory term of art under § 230, not a finding that Apple resembles a newspaper publisher.

The principal difference from O’Brien

There is nevertheless a significant distinction.

In O’Brien, the alleged wrong was Western Union’s transmission of a particular message. The carrier’s defense was that it should not be liable for faithfully performing its carriage obligation.

In Amy, the plaintiffs did not simply say Apple should pay damages whenever someone stores CSAM. They alleged that Apple had negligently designed iCloud by omitting automated detection technology. The proposed duty therefore required Apple to inspect the content of stored files. The court held that § 230 forbids imposing that monitoring duty through state tort law.

A common-carrier formulation would likely reach substantially the same result:

Apple may lawfully reject CSAM once identified, but its status as a neutral carrier would not ordinarily create an affirmative tort duty to inspect every private communication in order to discover unlawful material.

So, yes, O’Brien supplies a plausible parallel and perhaps a stronger nonpublisher rationale, but it was not raised or decided in Amy. The case proceeded entirely through product liability, negligence, statutory reporting duties, and § 230—not common-carrier law.

For thoroughness, Apple could have defended itself both according to § 230 and according to common carriage law.