Split phone signal

Hi,

I need help with a project. I need to build a simple low budget phone conference system. Most of it is done. The last thing I can't figure oout is how to split the audio signal because on the phone, everything travels through the same two wires. I would like to be able to monitor what people on the phone say (In an earphone) without hearing the meeting. Any ideas?

Thanks in advance for your help, Seb

Google for "hybrid transformer" or "balanced hybrid"

Thanks you for your quick answer, that's all I needed.

Seb