Purchasing an OBi wireless adapter is not the standard way of powering all your house phone outlets. It IS a way to connect an OBi 202 (not a 100 or 110) to your home network.
You are saying that you don't have a phone jack near where the current router sits, nor in reach of the OBi 100 that plugs into that router. Therefore, you have several options:
1) With a wireless phone that has a base and any number of receivers, plug the base into the OBi and all the receivers will work fine. No phone jacks needed.
2) Reposition your cable modem and router to be in a room near a phone jack. Often this is quite easy, you just need to know where your cable comes into the house, where it goes from there to the cable modem, etc.
3) Purchase a wireless distribution system (WDS) router, that is designed to connect wirelessly to another router. You can look on the Linksys site, but I suspect the router you have is not designed to do that.