Fellow blogger Ken Camp VoIPs from the road, and sometimes has as many as five mobile phones with him at one time.
To forestall backstrain, this self-described "digital road warrior" has switched to a Quantaray U-100 backpack used by many a photojournalist. They run about $80, and from appearances, are worth every penny.
Roll over the image, and you'll see where he's placed everything- including his travel headset for VoIP calls and podcasting. Not only that, but Ken's managed to pack a notebook computer, 24 AA batteries, handset adapter, digital camera with tripod, etc.
Based on preliminary observation of Ken's setup, I'd recommend that everyone who does VoIP from the road consider such a setup.
Ken, you're one organized dude.