I had an original Ooma device without WiFi built in. There's an Ooma adapter available for an unreasonable sum: $35, although it also has Bluetooth capability. I found a forum post that talks about how to use a generic USB WiFi adapter to turn the Ooma wireless.
The Netis WF2120 works and is only $7, but it needs some configuration. Plug the Ooma into a computer with an Ethernet cable via the Home port, not the Internet port. Then connect to http://172.27.35.1/ click on Wireless on the left and enter the wireless network's information.
Turns out my original Ooma is still alive, but the power brick died. I figured it was time to retire the old one, but it seems like they last for a while. The original unit I had for probably a decade.
