AT&T Inc said it has agreed to acquire privately held Interwise, a provider of voice, Web and video conferencing services, for about $121 million in cash.

The U.S. phone company said it expects to retain Interwise's management team and its domestic and international operations, including its R&D center in Israel.

The deal is expected to close in the fourth quarter. (Reporting by Saumyadeb Chakrabarty in Bangalore)