Calling USAA from overseas is difficult. In my particular situation, my cell provider will not let me call any of the USAA provided long distance numbers from South Korea.
My suggestion is to team up with Signal (by Open Whisper Systems) or Skype to offer USAA App built-in calling capabilities. This would offer secure communications at no cost to USAA or it's members. Difficulty or frustration in calling USAA would be all but eliminated for customers.
An alternative would be for USAA to offer a Signal number to call.