asterisk users - Nov 2005 - new sip domain support and REGISTER requests

hello,

since beta2 there is the new sip domain support - but somehow this 
feature is still a bit unclear for me.

routing to different contexts based on the domain in the extension.conf 
seems to be rather trivial, but is it possible to do the following things:

a) allow two users with the same name but different domains to register 
to asterisk. e.g. user@foo and user@bar.

b) if a) is not possible: is it possible to set the outgoing domain when 
a user places a call (the opposite of fromdomain).

bye,
gst