I've searched and seen some discussion of this on other threads addressing potential internet use on UA flights down the line, but none that exclusively focused on the question of whether UA should allow internet phone use once it introduces internet to its flights (whenever that is). So what do you think? And if you're against it, would you feel strongly enough to vote with your feet and choose an airline that bans it?

I strongly vote against it. It would raise the general noise level, the chances of having one or more passengers speaking really loudly, and the chances of getting stuck next to someone who even if speaking relatively softly might be going on for hours on end. I guess that all of these things sometimes happen simply with passengers talking to each other. But inflight internet phone availability could substantially increase the odds and frequency of them taking place, especially loud talkers since some cell phone users want or need to speak loudly to be heard.

If UA were to allow internet phone use I'd probably shift some or all of my business to any competitor that doesn't allow it.

Right now this is mainly a hypothetical question (except perhaps for p.s. service?), but with LH and other carriers introducing broadband access it seems that sooner or later UA will do so.