Getting the phone number of the trainer you started out with(Libby, Babs, Arbiters in Mercy) if that information is stored. If it's not stored, then it could be the phone number of Ms. Liberty, or even a new "mobile" trainer NPC who isn't in the game physically. When you call, it could open the same interface as a normal trainer, with all the information available that that entails, except maybe the ability to change builds
This could be extended to a mobile Freedom Corps person, or Fortunata. So that the difficulty could be changed out remotely.
*shrug* That's my idea...