Speaking while wearing Tefillin - revisited

Question

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?

Answer 1

The Vilna Gaon held (Maaseh Rav 18):

ולילך בהם כל היום אפילו משא ומתן מותר ואכילת עראי ג״כ מותר רק דברים בטלים אסור
And to go with [the Tefillin] all day, even business matters are permitted, and even non-fixed eating is also permitted, only useless words ["Devarim Beteilim"] are prohibited.

It seems like he's saying that regular actions that are purposeful are OK and one only needs to worry about unnecessary chatter. So if what you're saying has a constructive purpose, it should be OK. (Obviously, things which one shouldn't speak about without Tefillin on would remain prohibited while wearing Tefillin and moreover would likely also fall into the category of useless chatter.)

Edit: As regards the issue of non-fixed eating, Rav Chaim of Volozhin (in end note #4 to Tosefet Maaseh Rav) records that anything which does not require washing and the blessing HaMotzi does not constitute fixed eating in regard to Tefillin. (It is unclear to me if he is quoting the Vilna Gaon or not.)

Answer 2

This source refers to people who wear tefilin all day in our times. It says,

A small minority still follow the practice of wearing tefillin all day long. This custom is mainly found among followers of the Vilna Gaon and the Rambam, and among some Yemenite Jews.

Once in the Jewish Quarter of the Old City I saw two sights which may help answer.

1.) A yeshiva where the over-bar-mitzvah children were at break wearing their tefilin running in the playground. See this source, which says:

Batei Galicia [...] has been restored, and now houses a small yeshiva where the students wear tefillin all day.

2.) A bank where a man in tefilin was about to conduct a transaction.

I was told that these were followers of the custom of the Vilna Gaon.

So we see (according to their tradition) that it is possible to have a break from studies without being frivolous and banking transactions need not be frivolous.