Wow - this is a very heady project. I'm slightly envious of your getting to work on it, but mostly not because of my complete lack of experience or knowledge in the space.
You have some pretty high end demands/requirements. Just making copies of the SQL DB at the branches available at HQ regardless of branch status is not a simple task. Now you've just tossed on the fact that you need to rely on legacy hardware (Analog phone cards) and maintain - is it HA or FT or both?