No one can hear me
pushing the upper right key (the one below the lower right corner of the screen) when "mute" is written in that space, will put the phone on mute mode, similar to hold where you can hear the person, but they cannot hear you. Pushing the same key again (it will say un-mute if the phone is muted) will un-mute the phone, and the person on the other end will hear your call.
If that doesn't do it, call the person you got them from cause they are bum phones.
hope i wasn't too confusing and hope it helps.
If you don't have a cellphone headset, you can use any headphone cord i would think.