I.over [美 ˈoʊvər, 英 ˈəʊvə]副over often appears as the second element of certain verb structures in English (blow over, knock over, pore over, etc). For translations, see the relevant verb entry (blow, knock, pore, etc).
In this instance, there is no evidence that the defendants were in any way compelled to talk over their telephones, and were voluntarily engaging in business.