I'm new to this forum and have a question. I'm trying to interface both a cell phone and GPS to my Autocom motorcycle intercom. Autocom sells a special cable for $50, but I thought I could build my own for much less. Is this a simple matter of using 1:1 small isolation transformers to couple the inputs to the output? Obviously the cell phone connection is mic and speaker but the GPS interface is uni-directional mono (speaker) only. The Autocom cell phone interface has speaker in (center of 1/8" stereo jack), mic out (tip of 1/8" stereo jack) and ground (base of 1/8" stereo jack). What can I build (passive) to share the speaker input with both the cell phone speaker and GPS audio out, and perhaps in the future a radar detector? I don't want to spend the $50-$70 for factory cables. Thanks in advance for your help.