I have a remote site that is EZPVPN'd into the UC520 using a Cisco 861. The tunnel is up and running as expected. The 7921g registers and works as you would expect after it has been turned on. The problem comes in when you leave it idle, after a minute it seems like it loses connectivity to the UC520, but if the phone is left to itself, it will re register and work, then go "offline" again.
It is connected to a non Cisco AP at the moment. Could this be the issue? What else could be causing this to happen when connectivity is solid? Also a ping to the office gateway fromthat remote site is between 10ms and 40ms.