The cell phone network is a platform and it has no moderation.
If you want to decide what is acceptable content, you're not a platform, you're a publisher. A stated rationale for protecting internet platform providers was to provide true diversity of political discourse. It wasn't to make it easy to run a forum for Ninja 400 motorcycle fans.
You want to moderate content, fine, you're a publisher and you should be liable for the content you publish. The same way you would be if you published that content as a newspaper or magazine instead of over the internet.