Messages can be sent to Twitter from the 7x0i. Twitter is an available recipient (at least for a custom message). This does require linking your account at explore.garmin.com with your Twitter account. You do this from the Social tab. I have never actually TRIED this, but it is supposed to work.
There is similar functionality for Facebook. I have it in my head that the Facebook integration has been broken for some time. But I do not know why I believe that. I have never tried this, either.
Edited to add: This is the post about problems with Facebook. Apparently, you can post to pages you control but not to your timeline. I did notice that this is explicitly stated on the Social tab with the button for linking to facebook.
