I had my Band 2 for like 8 months, everytime I tried to call Cortana, it never worked. It would give some error, cant hear you (when it was right at my mouth and I was speaking at a strong volume), or I dont support that (a simple text), or some other error. It was a joke on how bad it was. Honestly, I got it to work 1-2 times in the 8 months owning it, I gave up on that feature because it was not dependable.
If you are going to use a feautre like this, it needs to work when you NEED it, not when it decides to actually work...
I moved over to a Pebble Time steel, and it has avoice text reply feature, I just hold a button, select the person I want to text (my wife is always first on the list because I text her the most) and hit voice.... and you want to know what ? On my Pebble Time, 99.9% of the time, it has worked flawlessly even in rooms with some noise, even with the radio on in the car...
Dont even bother using the feature, it's just not that dependable..