I also use Siri all the time for voice dictation and it's pretty good. The only reason to actually type a message on an iPhone, instead of voice dictate, is if

I also use Siri all the time for voice dictation and it's pretty good. The only reason to actually type a message on an iPhone, instead of voice dictate, is if you're in a place where speaking will bother other people or violate your privacy. Otherwise, press the microphone button and dictate what you want to write! It's also completely free, for unlimited use, which is worth keeping in mind.