welcome to the forum. when ur in ur contact profile, click the 4 corner on ur device and there should be something that says Link contact. once there u should be able to choose another contact to merge. mine did on the X and D2G
I am pretty sure you can not merge calls with two people you have on at the same time. You have to have one person on and then click the add call button on the dialer screen. That is the only way I know how at least.