If you have the password, it is fairly straightforward to change the IP address from a phone, just go into programming mode (spkr #*#*) enter the password and you can change pretty much anything you want. There are 2 possible IP addresses used to communicate with the outside world, they are in 10-12-01 and 10-12-09. Be very careful though if you change 10-12-09 it is the VoIP address and other equipment may be pointed to it. There is a third IP address that would need checking if you do change the VoIP address, it is for the DSPs and is in 84-26-01.