Question: May I say Kaddish by cellphone or Skype (a technology allowing one to make a telephone call (audio or video) using a computer)?
Answer: A teshuva (legal responsa) written by Rabbi Avram Reisner and approved by the Committee on Jewish Law and Standards of the Rabbinical Assembly of the Conservative movement concludes:
1. A minyan may not be constituted over the Internet, an audio- or video-conference, or any other medium of long distance communication. Only physical proximity, as defined, that is being in the same room with the shaliah tzibbur, allows a quorum to be constituted.
2. Once a quorum has been duly constituted, anyone hearing the prayers being offered in that minyan may respond and fulfill his or her obligations thereby, even over long distance communications of whatever sort.
3. A real-time audio connection is necessary.Two-way connection to the whole minyan is preferable, though connection to the shaliah tzibbur alone or a one way connection linking the minyan to the individual are sufficient. E-mail and chat room or other typewritten connections do not suffice. Video connections are not necessary, and in the absence of audio would not suffice.
It is clearly not preferable to join a minyan by skype. There is a deep danger that too many people would choose to skype in rather than physically participate, thus putting the minyan in danger -- note that a minyan requires 10 people physically together - the skyped people don't count. There is a another potential time zone problem if, for example, a minyan is in the Boston area and the skyped participant is in Amsterdam. How can one participate in a particular minyan when the time zone in their home location would suggest a different minyan -- shaharit vs. minha, minha vs. ma'ariv? Rabbi Reisner suggests that one should participate in a minyan within one’s own time frame.
Note that this teshuvah applies on weekdays. Shabbat presents an additional set of issues with the use of technology.