Segment sms send does not work, because some exception gets triggered. The reason you do not see the exception is because the sending is wrapped in try catch block.
We need to fix the underlying issue and change the try catch block, until then only campaign sms send is working.
I guess it might be something to check. If you are trying to put the telephone number in the field, that is wrong. You have to set the messaging service ID now (obscured in the screenshot below).