How to make a 3 way call

When you phone someone on an android you should be able to phone another person after the first call by pressing the + icon on the call menu screen, then there should be a merge icon that should look like 2 lines merging to one with an arrow, that will merge the calls.

Edit: I don't know how these kinds of calls are charged, but I'd say you might be charged for two separate calls at once.

Hope this helps.