Asterisk is, the most feature-rich open source Software based PBX phone system on the market. As a result of it's open source nature it is less expensive. Asterisk run on Linux like platforms. For a view of some of the phones it can use click here.

Talkswitch is, a very good switch where there will never need to have more than 20 phones. This is a propriatary hardware system that uses analog phones and SIP for interoffice connectivity. Talkswitch also has fewer features than software PBX's.