Kind of a Bug re SMS
I'm not sure if something like this should be reported like this or by private message.
I just went to enter my phone number for SMS. Your choice of numbers "Number to send from" are in international format - i.e., "+1....."
I just assumed that since you had used international format at one place on the page, you were expecting the destination number to be entered in international format. It didn't work, and by trial and error I found you wanted just the 10-digits.
Yes, I now see the fine print shows you just want the 10 digits.
I think you should either show the originating number choices in 10 digit format, or allow entry of the destination number in international format. The current way of doing it is internally inconsistent.