OMA authorizes a member of a public body to participate in a public meaning by a conference telephone or similar communication when it is otherwise difficult or impossible for the member to attend the meeting 

(emphasis added). NMSA 1978 § 10-15-1-C

If a conference telephone is used, each member participating remotely must be identified when speaking, and all participants must be able to hear each other at the same time and members of the public attending the meeting must be able to hear any member of the public body who speaks during the meeting. The latter rule also applies when all members of the public body are present at the meeting — sidebar and secret conversations during the meeting are impermissible. NMSA 1978 § 10-15-1-C