Serial Brige for IP-phone system

It is designing IP-phone system. It is take some information from controller from serial port and send this infromation to another device. Becouse this system must be like phone system, it’s must send information from device with one IP to device with another IP. If I don’t mistake, I can use Serial Brige mode on Digi ME. And I have question - where are writing IP-adress of device of recipient (it is very impotatn to design IP-phone system, for example, we have 3 device with IP # 1, 2, 3. At first time we can connect IP1and IP2, and at secind time we can connect IP1 and IP2. All Digi’s modules emmbeded in the controllers with RS-232).