In today's day and age the vast majority of the time we only wear Tefillin when we are Davening. However, in theory, we should wear them all day (ibid). So what about the requirement not to speak frivolously in them? What exactly is considered frivolous? Are Divrei Torah frivolous? Let's assume not; I know a few people who learn all day and don't take off their Tefillin until the first time they take a break from learning. But what about general greetings? How is one supposed to conduct business affairs, even assuming one is very spiritually oriented and focused LeShem Shamayim throughout the day, how does one avoid general conversation - or does frivolous mean more degrading types of conversation? Then, even assuming that that is what it means, what about eating and drinking? What about wearing them during some kind of celebration - at a Berith Millah most people wear them, but what about a wedding where one is obligated to dance before the bride?
I know I've listed several different scenarios which might have different rulings, but I'm trying to get to the bottom-line answer of what exactly is considered too frivolous for wearing Tefillin?