Asterisk aka *
This is a very powerful PBX software designed so you can build your own mini-exchange like in use in large companies. it scales very well and is extremely powerful. It has support for all sorts of protocols and lets you dial internal or external users and trunk calls in various ways.
NathanWard is writing some proper billing and rating software for *, also some better VoIPLeastCostRouting software. He would like to use it at Quicksilver Internet in his VoIP infrastructure.
LindsayDruett would just love to try with the Cisco IP Phones, VoIP Gateways, etc with this software, basically use it as an alternative to the CiscoCallManager using the Cisco Products but without the baggage like product distribution curfews, etc. Also product licensing costs would be substantially cheaper as you can then purchase IP Phones without the CiscoCallManager user licence.
Apparently the Cisco IP Phones are part of the product distrobution curfew.
Note that if your Asterisk machine is connected to a PABX, that's fine (assuming your PABX has a telepermit), but if you're connecting directly to your phoneline, you need to make sure your FXO/FXS device is telepermitted. To the best of my knowledge, not many of the devices are. If anyone knows, list the legal ones here....
