How to get two sims to live together from different familes?

Far as I know there should be two ways. Use the phone, as you suggest, to split the household and move some out.
The same, or at least a simlar effect can be achieved by going to "Manage Worlds" and then into Manage Households. You will reach a screen which shows you all the families living in your save. They will be under two categories, played and unplayed/other. By selecting the appropriate option there (I forget the exact wording, sorry), you will be able to move Sims around between households.
Hope that helps.