Is it absolutely necessary to install the Cisco Unified Communications Manager to use/setup the Cisco Unified Wireless IP Phone 7921G ?
Or can I just connect the phone to the Internet and get incoming SIP calls directly from the VoIP provider?
That would be a question for the supplier that you purchased it from...
Otherwise there is a healthy market for anything with a Cisco badge on ebay, and lots of specialists dealing in used kit all over the world.
The 7921 only supports SCCP which is Cisco's proprietary signalling protocol. Same applies for all the Cisco 792x wireless models as far as I'm aware.
So no, you can't connect it to a SIP provider. There are probably other manufacturers out there doing SIP wireless handsets that would be more appropriate, and likely cheaper.
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