It is forbidden to speak after the recitation of Kiddush until one partakes from the wine. This applies both to the person reciting Kiddush, as well as to the others at the table who fulfill their requirement by listening to his recitation. If they intend to drink from the wine, they may not speak until they drink. This applies to the Beracha of Hamosi over the bread, as well. After one recites the Beracha, he may not speak until he eats a piece of bread, and the others may likewise not speak until they partake of a piece of bread.
Must one repeat the Beracha if he spoke after the Beracha and before drinking the Kiddush wine (or, in the case of the Halla, before partaking of the Halla)?
If the person who recited Kiddush spoke before he drank the wine, then he must, indeed, repeat the Beracha. His speech disqualifies his Beracha, thus requiring him to recite a new Beracha of "Boreh Peri Ha’gefen." The others, however, who listened to his Beracha and recited, "Amen," may drink without reciting or hearing a new Beracha. Their listening to the Beracha and recitation of "Amen" amounts to a personal recitation of the Beracha, and thus they are not affected by the interruption made by the one who recited Kiddush. Hence, although he must repeat the Beracha, they may partake of the wine without listening to or reciting a new Beracha. Once again, this applies to the Beracha of Hamosi, as well. This occasionally happens when as the individual is slicing the Halla after reciting the Beracha, he makes a comment about the texture of the Halla, forgetting that he may not speak until he eats.
The Halachic authorities debate the question of whether one of the other people at the table must recite a new Beracha if he spoke before partaking of the Kiddush wine. This is a very common case; quite often, as the people around the table wait to receive their wine, or their slice of Halla, they grow restless and begin speaking. Must they recite a new Beracha in this case, or can they still rely on the Beracha that they had heard?
This issue is subject to a debate among the authorities. Some maintain that since the one who recited the Beracha remained silent until he partook of the wine or the Halla, the Beracha was thus effective and cannot be disqualified by the subsequent speech of one of the other people at the table. Others, however, disagree, and claim that one must indeed recite a Beracha if he spoke while waiting to drink the wine or receive his piece of Halla. As for the final Halacha, the Ben Ish Hai (Rabbi Yosef Haim of Baghdad, 1833-1909) and the Kaf Ha’haim (Rabbi Yaakov Haim Sofer, Baghdad-Israel, 1870-1939) apply to this case the famous rule of "Safek Berachot Le’hakel," meaning, that we do not recite a Beracha that is subject to doubt. Since there is some uncertainty as to whether one should recite a Beracha in such a case, it is preferable for one not to recite a Beracha, and partake of the wine or bread relying on the original Beracha.
Of course, one should endeavor to avoid this situation, and ensure not to speak until after he partakes of the Kiddush wine or the Halla.
Summary: It is forbidden to speak after Kiddush and after the Beracha over the Halla until one partakes of the wine or the Halla. If the person who recited the Beracha spoke before he partook of the wine of Halla, he must repeat the Beracha of Ha’gefen (in the case of Kiddush) or Hamosi (in the case of Halla). If somebody else at the table spoke before partaking of the wine or Halla, he should nevertheless drink the wine or eat the Halla without reciting a Beracha.
