Originally Posted by
SoManyMiles-SoLittleTime
Thanks for this excellent response. It suggests the method I would have come up with if I were blank-sheeting a design. I'm assuming the renewal process is very short, otherwise there is a window of missed-call possibility. It also suggests that a static IP address is indeed a (perhaps only slightly) better way to go.
No, you can ignore the posts here that refer to Dynamic DNS - this is not relevant to what you are asking.
ATA devices generally use a protocol called SIP. When you plug the device in, regardless of your IP address, the ATA will contact a registration server, tell it who you are and what your phone number is. It periodically performs this process, and the server can see what IP address the messages are coming from. This is what forms the phone number <-> IP address matching.
Generally, the only time your IP address changes (if it does at all) is when the Internet connection is dropped or re-established. In these situations the SIP device just re-registers itself from the new address and works as normal.
You should have no issue using the device when traveling, provided it is connected to an "open" Internet connection. If you have to perform some sort of authentication first (like on a hotel Internet connection for example) then you may find it more tricky to get working.