Is it possible to have a phone without a voice plan?
Since the cell network was originally built for voice, the cell companies kind of have a focus on voice. While this might be technologically possible, I can't imagine how you'd convince a cell phone company to sell you a data-only plan for a device that supports voice. I'm not sure it makes business sense for them to do so - after all, why not rip you for at least a little voice, along with the data. If you don't use it much, then so much the better because they save on capacity.