I wonder why someone would want a single phase electricity?
Our meters calculate peak load n a factor is applied to over all energy bill so watch out for that. Wapda is bloody loot, they have included many surcharges in a bill so try to avoid those. So never opt for single phase if u have more than two electric appliances ie fridge, ac and iron+kitchen machines etc. If ur load is equally distributed like if u have 1 fridge, 2 ACs and other house holds then distribute each load on each phase that will reduce extra units consumptions.