[luv-talk] Office telephony - Asterix, VoIP, etc.?

Hi all (and happy new year!), Does anyone have any pointers on setting up an office for 3-4 staff with a simple solution, preferably open-source based? I'll be setting up a new office in about 4-6 weeks; I expect I'll have Internet with someone like TPG, which includes both Internet and a phone line. I imagine I could run a second line using VoIP (with some degradation of audio quality); presumably Asterix or something similar could manage 3-4 phones running over 1-2 lines like this. Is there a package/solution people recommend? I'd like something reasonably resilient and easy to set up - I don't want to spend hours playing around with it, but the idea of an open system I can customise and extend is attractive. thanks! Nathan