Earbuds don't answer phone

[Nedrod]

I have attempted to use earbuds to answer my iphone 4. The first pair were Zagg buds and didn't seem to work. Since I had them for several years, I thought they may be defective. I purchased some new Sennheiser buds but they don't seem to work either. Is there a way to test the phone to see if it may be the problem? I don't have the buds that came with the phone.