The i62 is WiFi, the d62 is the Dect version. These are very robust phones. They cost a lot more than others, but they can withstand a lot of abuse. I would say the battery life is good. Users in my case can go an entire shift without swapping batteries.

My system came with an AA50 from Digium, but if you already have an Asterisk system to hang your phones on, then you shouldn't be buying an Asterisk box with this system. I guess it doesn't hurt, but you don't need it.

I would recommend the UPAC, especially with the Dect phones. The UPAC provides features that you normally wouldn't have, such as messaging and PTT.

In my case there are issues with the analog integration that we are still working out and the AA50 has been buggy, but if you are pure SIP and you have a stable Asterisk deployment then I think it's a great system.

Just a note that you can find nearly identical phones from Aastra and Ericsson. I'm not sure who own what and who builds product for who, but they all have interchangeable products for Dect and WiFi.