I think I may have just found a little bug.
I have 2 Telo handsets. I bought the first one back in December and just got another last week. The following applies to both handsets:
During a call, I sometimes want to decrease the handset volume. If I press the square button on the handset downward slowly, all is ok. However, if I press it a few times in rapid succession, it then becomes impossible to disconnect from the call, as well as impossible to power down the handset. The only option left is to disconnect the battery.
I came across this by accident, but later was able to replicate the identical situation multiple times. It's not something that's critical, but it may be an item that Ooma needs to include on their future fix list.