Is it ever permissible to say Kedusha in the middle of Shemoneh Esrei?

As we have learned, a person who did not start Shemoneh Esrei with the  tzibur may not begin unless he can finish in time to respond to the devarim shebekedusha. If he began Shemoneh Esrei when the chazan began Chazoras Hashatz, however, he may say all of Kedusha along with the chazan, followed by L’dor V’Dor until Hakel Hakodosh. Afterwards, he has a choice. If he can complete Shemoneh Esrei before the chazan reaches the end of the brocha of Shomeya Tefilla, he may continue on his own. Otherwise, he should continue reading along with chazan until after the brocha of Modim. Some poskim say that this option is preferable. Shulchan Aruch and Rema both rule that the method of davening along with the chazan is generally b’dieved, and l’chatchilah one should wait to begin until he hears all of the devarim shebekedusha.

סי' ק"ט ס"ב ס"ק י"א-י"ג

Is davening along with the chazan considered tefilla b'tzibur?

Other Achronim disagree with the Shulchan Aruch and Rema and rule that even l’chatchila one may choose to daven Shemoneh Esrei along with the chazan. Many Achronim rule that davening with the chazan is like davening tefilla b’tzibur. Others say that it is not equivalent to tefilla b’tzibur but it is a step above davening by oneself. If one did not start Shemoneh Esrei together with the chazan but happens to reach Kedusha with the chazan, he should still respond to Kedusha. If he hears Kedusha from another minyan, he may answer but he is not obligated to do so. One should not answer to the Kedusha which is recited in the middle of U’va L’Tzion or Birchos Kriyas Shema, even if he has reached the Kedusha of Shemoneh Esrei at that point. If he is in the middle of Shacharis, he may respond to the Kedusha of Musaf.

ס"ק י"ד ביה"ל ד"ה אם וד"ה שאין ביאורים ומוספים דרשו 23 27

Is a person who is davening along with the chazan obligated to adopt his nusach?

The following are assorted halachos for one who is davening along with the chazan: 1) He is permitted to raise his voice during Kedusha. 2) He should raise his heels when he says Kodosh. 3) A resident of Eretz Yisroel who is davening a weekday Shemoneh Esrei may say join with the chazan in reciting the Kedusha of Yom Tov. 4) If he is used to davening a different nusach than the chazan, some say that he must change his nusach for the entire Shemoneh Esrei. Others say it is only necessary to adapt for the first three brochos. 5) He should not say the additional piyutim which are recited on special occasions. 6) Most poskim say that he should answer Amen to Birchas Kohanim. 7) He should not say Elokeinu before Sim Shalom together with the chazan. 8) He should say V’searev along with the chazan.  

ביאורים ומוספים דרשו 19 20 21

• One may not begin Shemoneh Esrei if he will not be done by the time the chazan reaches Modim. Otherwise, he may find himself in the middle of a different brocha and will be unable to bow when the tzibur is bowing. According to the Rema, a person may only start if he is certain that he will not still be in the middle of Shemoneh Esrei when the chazan reaches the end of the brochos of Hakel Hakodosh and Shomeya Tefilla.   

• If a person estimates that by replacing the brochah of Sim Sholom with the text of Sholom Rov he will finish davening in time for Kedusha, the poskim disagree about whether replacing the text is permitted.

• Although there is a halacha that one must travel a certain distance for tefilla b’tzibur, there does not seem to be any such obligation for responding to devarim shebekedusha. 

• Under what circumstances is it permissible to daven a shortened Shemoneh Esrei?

• Is it ever possible to daven Tefillas Havineinu on Motzei Shabbos?

• How much time may a worker take off from work to daven?