Dual Sim but one outgoing number
For this I recommend using Skype Out. you can authorize skype to give your actual cell number as caller id when making a Skype Out call. I do this when travelling overseas, my outgoing calls say they are my US number. I let incoming calls just go to voice mail of my real cell phone number so I don't have to pay international fees, and immediately call people back using skype out. My clients never have to know I'm out of the country.