Last week I helped a friend with a new (Verizon) X set up Google Voice. Everything went fine, including switching to GV as his voicemail service.
HOWEVER, we then started looking carefully at the menu, and I realized that there were no options to compose a text message, nor an inbox to view past ones (indeed, texts that he already had from using the same GV account on a PC). In other words, it seemed as if someone (Verizon?) had vacuumed out the SMS function.
Perhaps it didn't install correctly -- I've never seen anything like that, but my first impression was that "Verizon blocks text messaging within Google Voice."
Can anyone else confirm they've got it working on the Moto X?