While I have been shopping on eBay for new adapter, I noticed quite a few listings where people sell "travel case" for OBI adapters. Here's just one example: https://ebay.us/auwBwS . I'm very curious, why would anybody need travel case for VOIP adapter? is it something people travel with?
Yes. You can connect an OBi to the internet in most* countries to make and receive calls just as if you were at home.
(* some governments and telcos forbid or block VoIP)
A travel case for an OBi is for people who don't own a paper or plastic bag.