One final note to close out this topic of brachos of tefillin. The Rishonim discuss what the halacha would be if there is a hefsek between hearing all the kolos one is required to listen to on Rosh haShana, and the general consensus seems to reject any comparison to speaking between tefillin shel yad and shel rosh. The Rosh (R”H 4:2) writes that tefillin are two separate mitzvos, and unless hefsek is avoided there would be no relationship between the shel yad and shel rosh. Additionally, the shel yad and shel rosh require two separate brachos; if one speaks between them, the connection between the brachos and the two parts to the mitzvah is broken. The Ba’al haMaor (last daf of RI”F) goes a step further and writes that the command “v’haya l’os al yadcha u’lzikaron bein einecha” demands that one havaya be created with both tefillin – in other words, the Torah commands that both tefillin be donned together as one unit and not as discrete parts. By shofar, there is no inherent dependency of one kol on another.
There is a fundemental difference between Rabeinu Tam’s position and that of the Ba’al haMaor. According to Rabeinu Tam, hefsek must be avoided because it separates the brachos from the mitzvah act; according to the Ba’al haMaor avoiding hefsek is an independent consideration from the brachos. When tefillin are worn without a bracha, such as on chol hamoed, or those who don tefillin of Rabeinu Tam daily, according to Rabeinu Tam a hefsek might be tolerated, but according to the Ba’al haMaor it should still be avoided.