The 8821 is a fairly new phone released to the market, however, like other corded phones this unit supports SIP.
One can use a computer to configure the WLAN settings of the phone and it will work, however, no one has yet tried integrating this with non-Cisco call manager/server (like Asterisk-based or 3CX). I have no doubt this will work but it's just spending time trying to knot out the kinks.
Just want to warn you that due to the "freshness" of this product, you must keep an eye out for new firmwares for the phone. The current firmware still has a lot of bugs that is constantly being ironed out.
