Although Cisco makes a nice line of phones, we don't recommend them for our customers because Cisco does not plan to continue to support SIP on them. They will continue developing SIP support on their Linksys branded phones, which we've tested out and really like. However, as a courtesy for customers who already have Cisco phones, we published a Knowledge Base article on how to get them set up and configured for our OnSIP Hosted PBX, which you can find here. Note: We were wrong. Cisco will continue to develop SIP for their Cisco line of phones. However, the Linksys phones are easier to configure and manage, so we still recommend avoiding the Cisco line if you have not already purchased your phones.