Hi Electricman,
What's IRDA? Do you have a link or can you describe what the letters mean?
It is difficult to have loudspeaking, full-duplex two-way communication. Acoustical feedback occurs unless the speakers are turned way down in volume and the mics are not very sensitive. If the mic can hear you, it can also hear the speaker near it.
You speak into your mic, it comes out the speaker at the other end. The mic at the other end hears its nearby speaker sounding your voice and sends it back to you, and around and around the sound goes.
Old intercoms and speakerphones used voice-switching, where your speaker gets cutoff when you speak into your mic. If you keep on talking or if it is noisy at your end, your speaker is cutoff permanently and you won't hear the other end.
Newer intercoms and speakerphones use acousical echo cancellation DSP to try to eliminate feedback. When they get out of whack by the room conditions changing by a door being opened or people moving around, they make cool space-age noises.