The line port on an OBi110 is used to connect to a PSTN (landline). You can use a splitter plugged into the phone port of an OBi200 and connect it to a phone and the wall jack. You can't use any USB WiFi adapter on a OBi2xx, you must use the OBiWiFi adapter.
Edit:
There isn't a lot of room on the back of an OBi200. It would be better to plug the splitter into the wall jack and then connect the OBi200 and a phone to the splitter.