Someone correct me if wrong but I think phone co's can get away with it as they're deemed an information carrier instead of a host. Besides, calls and texts are rather benign, it's visual media that tends to attract the most calls for censorship, not to also mention that real-time censorship of text and voice would be infeasible but much more viable for an information/media host.
And phone companies don't play an editorial role in determining what calls you get to hear, and who hears yours. Newspapers are responsible, even when they're publishing someone else's submission to them.
