Check out the latest SIP endpoints from Panasonic which were showcased in this video this past month at ITEXPO in Los Angeles. The TGP500 supports up to 6 additional SIP endpoints and 8 SIP registrations - it even works with
Asterisk. There is key-set integration, barge capability and lots of other functions allowing an SMB to seem like a large enterprise. This solution is a great cordless add-on to another system according to the company.