Quality of VoIP is lacking IMHO. I generally use a simple speaker phone or headset if I need to be mobile. I made sure my office was designed in such a way that the acoustics of a speaker phone wouldn't sound hollow or echoey. Lately I've been using my iPhone. I can do everything including setting up conference calls. A portion of my calling is international and I haven't had any problems yet. I can't dump my landline because some people still use fax machines.
Just a tip if you've never worked from home before, wear shoes. It gives you purpose.
