The Pirahã also have an unusual counting system (none). http://itre.cis.upenn.edu/~myl/languagelog/archives/001364.h... ...but this cuts against the argument that the medium very much influences the message.

I've heard the argument that some of these channels may be influenced by the jungle environment (whistled language elsewhere is frequently used outdoors because whistles carry farther). And I think whistled or musical speech is likelier to occur in tonal languages with a simple phonology (Pirahã's is very simple and very tonal). Dan Everett's claim was that a cultural avoidance of indirect references influenced the grammar of Pirahã (to put it crudely).