Things I found out about call waiting
My apology if similar threads had been posted, I just would like to share what I found about handling call waiting calls in my Z10. I anticipate this will also work in Q10?
If you are on a call, and another call comes in. A green and a red phone call button pop up. Press the red button will reject the new incoming call and send it to voicemail. Press the green button, as expected, will answer this new incoming call and put the first call on hold. What I found interesting is, if you press and hold the green button, it toggles to an option which you can drop the current call and answer the new incoming call. If you changed your mind, press the green button again, will toggle it back to putting the current call on hold option.
Say now you have first call on hold and talking on the second call, press the big red End Call button will end the second line and switch back to the first one. However, if you would want to keep chatting on the second line and drop the first call, all you need to do is touch and hold on the avatar of the first call (a smaller one on the left side), a message will pop up and ask if you would like to drop it. Click OK and the first call is dropped and you can continue with your second call.
Hope this helps.