I haven't seen this mentioned anywhere on the internet yet, so I felt a need to share...
I googled for "droid incredible 4-pole" and found one Verizon document mentioning that the connector is a 4-pole connector (it is not in the user manual). My iPod earbuds were not giving me any reception. So, I used a 4-pole to 3 RCA cable from a camcorder, paired with a 2 RCA to stereo 3.5mm (3-pole) cable attached with:
stereo L -> white
stereo R -> yellow
The red cable I left unconnected. If I tried touching the red signal pin to ground, it caused the radio to reset, or the phone interpreted it as a "start voice command" button. I don't have one around to test with, but I think that the wired hands-free sets are 4-pole 2.5mm connectors, and the 2.5mm plug might fit loosely in the 3.5mm jack?
I tested continuity with a multimeter between all three signal pins and they are definitely distinct.
Anyway, I get great reception now. I just need to figure out a more compact method that doesn't involve 8 feet of cables in my pocket.