I don't think you can do it that way. I think you have to initiate both calls.

 

In practice, I think you are correct. In principal, I read in the manual that when you recieve the second call you just need to click the "add call" button. I have not tried it, nor even checked to see if that option comes up.

I know that was the ONLY thing I liked about my old AT&T iPhone. Conference calls were easy. Of course, once you got the conference going, the network wohld drop one or both of the calls. So, it was pretty useless in practice.

 

I've never done it, but if you Google "Android 2.2 User Guide", you can view or download a copy. On pages 79 through 82 it covers handling multiple calls and doing conference calls.