The Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), in Parashat Nisavim (12), writes that the Toke’a (person blowing the Shofar in the synagogue on Rosh Hashanah) should verbally declare before blowing the Shofar that all the sounds he blows should fulfill the Misva obligation for himself and the congregation. Even though it is obvious and self-understood that this is the purpose behind his blowing the Shofar, he should preferably express this intention verbally, rather than simply thinking it in his mind.
The Ben Ish Hai then proceeds to discuss an important Halacha of which unfortunately many people are unaware. Namely, that neither the Toke’a nor the congregation may speak at any point from the time the Toke’a recites the Beracha over the Shofar until after the final Shofar blast is blown after Musaf. Needless to say, conversing during the prayer service is inappropriate at any time, and one must avoid talking from the beginning of the service until the end. In the case of Shofar blowing, however, this prohibition assumes even greater importance. The reason why we blow the different kinds of sounds is because we are unsure of precisely what kind of sounds we should blow. In order to ensure to fulfill the Misva satisfactorily, we blow every possible sound. Therefore, every Shofar blast that is sounded may be the one through which we fulfill the Misva, and one may not speak in between the Beracha over a Misva and the performance of the Misva. It is therefore imperative that one remain silent from the time the Toke’a recites the Beracha over the Shofar until the final sound is blown.
The Ben Ish Hai goes so far as to say that the Toke’a should not recite the verses and hymns that we customarily recite as we return the Torah to the ark (such as "Hon Tahon"), as this would constitute a "Hefsek" (interruption). The custom in our community seems to be that the Toke’a does recite these verses and hymns, but this ruling underscores the seriousness of this Halacha, and how important it is to remain silent throughout the service once Shofar blowing has begun.
Furthermore, Hacham Ovadia Yosef ruled that one should not recite Vidui (verbal confession) in between the sets of Shofar blasts. The Ben Ish Hai advocates following the custom of making verbal confession during the pauses in between the sets of Shofar blasts, but Hacham Ovadia disagrees. He maintains that although one may certainly think thoughts of repentance in his mind during these pauses, one may not verbally declare confession, as this would constitute a "Hefsek." If even confession is deemed an unwarranted interruption in the Shofar blowing, then certainly speech and conversations unrelated to the prayer service must be avoided.
Summary: It is strictly forbidden on Rosh Hashanah to speak from the time the Toke’a recites the Beracha over the Shofar until the final Shofar sound is blown after Musaf.
