Glad to hear about the domains.

So far, the features look great. You've covered the major necessities.

I'm sure you already have plans for more, but here are some features to consider.

music on hold, custom would be nice, but built-in should be fine initially
improved date selection tool in call history
more flexible date and repeating pattern options in the scheduler
star codes to access/change recordings from phone rather than control panel
other star codes... paging, intercom, transfer, park, echo test, clock, weather, etc.
virtual conference room extensions

maybe call queues, but I could live without that on this type of system

Others will likely want call recording, but this isn't high on my own priority list either.

White box customization (logos, colors, menu customization, etc) would obviously be nice.

Maybe combine the numbers and gateway functions to make it all more intuitive for novices.

That's all I got for now.