Summary: Using Ubiquity access points with "zero hand-off" enabled makes these phones not connect to the network at all. They'll scan, see the network, try to connect, and get stuck there.
Pros: The phone has a wonderful display, and everything my customers love about the SPA5xx line. They look good, sound good, and perform well.
Cons: The provisioning interface (web gui), while adequate, looks absolutely nothing like the rest of the phone's series. It's OK, but different. I don't understand why you'd make a whole series of phones, then change that on ONE of them.