Sip Phone Plugin

Can someone describe to me how this plugin works? Does it use Spark as a soft phone? Is there a way to have a person choose to call another person in their contact list via a VoIP phone? (user chooses to call someone from their contacts and their phone rings then the other party’s phone rings).

We are using Openfire in our company and are migrating to a hosted VoIP solution (using Polycom phones) and would like to have some sort of integration (similar to what I’ve read with Asterisk).

Any input would be great!!!

Thanks.