i have one HQ in England and its branch in U.S ... in both locations i have 5digits of extension ... both are connected to each other via MPLS and on Branch there is an E1 link for SRST ... users from HQ should able to make call to Branch via 5digit extension but if Branch user's want to call HQ they must dial 5digit extension but that 5digit ext should replace in International Number & call should go to HQ via E1 PSTN Cloud.
(means call from HQ --> Branch via 5digit extension, or from Branch --> HQ via PSTN)
how we can do that ???