PaulB wrote:So... If I dial 999 or 112 now:-
- will the handset jump networks if it needs to?
Yes. If your subscribed network isn't available, but another one is, it'll come up with "Emergency calls only" on it.
PaulB wrote:- would an existing call be disconnected to allow the emergency call or would the emergency call get an engaged tone?
It's a bit of a moot point now with 3G voice capacity being so large, but theoretically yes, another call could be dropped.
There are also different classes of SIM card which are given priority in the network, so, for instance, if emergency workers were issued with phones, they could have a class which takes priority over other phones regardless of whether an emergency number is being called or not.