I've got power, but it won't auto-register. Other phones work great.
Did you do all of this:
How do I sync my Ooma Telo Handset with my Ooma Telo?
To register your Ooma Telo Handset, first visit https://my.ooma.com/pin to retrieve the PIN number for you Ooma Telo. Note that you may need to log into your My Ooma account when you visit this webpage. Next, bring the handset close to the Ooma Telo and press the (A) key on the front panel of the Ooma Telo for 3 seconds. The (A) key should start flashing rapidly as the Telo searches for new handsets. Within a few seconds, you should hear the handset beep and prompt you to enter a PIN number. Enter the PIN found at the website above and press OK. The handset will notify you when it has finished registering. The first time you register a handset, it may need to download new software. Ooma recommends that you place the handset in the charging cradle while the handset is loading the software upgrade.