AT&T fought tooth and nail to prevent telephones manufactured by third parties from connecting to their network, and eventually lost. Why should the major digital communication platforms fare any differently?
- Hush-a-Phone Corp v., United States[0], in which the DC Circuit Court of Appeals ruled that AT&T could not prohibit the mechanical attachment of a device to its phones as long as the device did not damage AT&T's phone or its network
- The Carterfone decision[1], where the FCC allowed third-party devices to be electrically connected to AT&T's network as long as they did not damage the network
[0]: https://en.wikipedia.org/wiki/Hush-A-Phone_Corp._v._United_S...
There are a zillion messaging clients... Signal, Slack, Discord (all of them work on iPhone)... Sms is a protocol, iMessage works with that (it is connected to the network)...
As an aside, the old ATT phones were nearly indestructible. Everything that came after was a race to the bottom.