Network system and method for facilitating message exchange between mobile subscribers belonging to the same or different public land mobile networks, possibly incorporating different standards. Message exchange between two subscribers of the same or different networks may involve one or more lookups on subscription data, zero or more message transformations, one or more routing decisions including application of costing functions, and, storage and propagation of the message in one or more Core or Intermediary networks. The messages may be of type, among others, SMS (Short Message Service), MMS (Multimedia Message Service), or EMAIL. An aspect of the present invention provides a message routing subsystem that facilitates destination determination and delivery channel selection.