Modbus RTU using phone number instead of IP

[russ]

Using an RV-50X, is it possible to setup Modbus RTU to use phone numbers instead of IP? This customer did not get static IP SIMs, so the only constant is the phone number. My PLC devices are serial devices and only use Modbus ID (like station 1 or 2), so can the Address List use phone numbers, or is there some other way to use phone number rather than IP?