Why do some earphones work but some have garbled audio on my phone?
The pin layout between the working and not working head phones might be different and hence this behaviour.  Though it appears to be simple there is no one standard to which all these manufactures seems to stick with. For instance my LG P500's stock ear phones exhibit this issue with Sony Ericsson SK17i, while Sony's head set played well in my LG P500.  

The same problem exhibits when I use my LGP500 head phones in my desktop computer. While doing so, I just pull out the head phone slightly out to solve this issue.