Call between two different PLMNs

Archived from groups: alt.cellular.gsm (More info?)

hi there,

what happens exactly when a mobile station (MS) from PLMN 1 calls a MS from
PLMN 2 ?
I'm trying to answer this easy question, but all I found in several GSM
books are the "Mobile Originated Call" and the "Mobile Terminated Call"
procedures, which both explain the scenario of a connection "MS with ISDN
subscriber".

I think there must be an interaction between the two GMSCs, but how does it
happen?
Is there anyone who knows the details of this situation?

thanks