>If the T1 goes down, we'll queue up the changes and update the customer file when the T1 is back (at least, that's one solution).

That's one solution.

>
>What approach would you take to this? Maybe have a centralized customer file (at Company C) containing customer from both companies, that would update their respective company databases... what, in batch mode overnight? The Order statuses need to be reflected in real-time.

I don't have enough information to recommend one approach over another. I'm just throwing out some questions.