1) One may not interrupt with speech between the blessing of Yishtabach and the blessing of Yotzer Or, and one who does, has committed a sin. However, for communal needs, or for charity, one may interrupt. (Shulchan Aruch 53)
2) Between Kaddish and Yotzer Or one may not interrupt even for communal needs and charity, since the saying of Kaddish and Barchu are considered an integral part of the blessings of the Shema, in which one may not interrupt. (ibid)
