forgot to answer this one earlier.
- depends on certain factors - which exchange, did the exchange report back your position, etc. perhaps orders can and/or are be input via the globex or other exchange supplied terminal but i'm not sure of the procedure. we'll do it in HK but if we had hundreds of calls at the same time, it would be overwhelming.
-. If the prop side system is down, the only way out of a trade is via a floor broker in the open outcry markets and/or via the front end of the exchange system is down. On the prop side there may be a hundred thousand open positions at any time, it is not micromanaged if there is a system problem.
-. in markets that are fully electronic and the link goes down (i recall about a year or so ago in HK, half of the exchange was shut out due to construction that knocked out both main and backup lines), if you want out or in a trade you need to call another broker.
-. someone asked about institutuions. Institutions tend to have more than one broker. If they need out of a trade they typcially will use another front end or broker.