Dual Sim but one outgoing number I have a dual sim phone and am starting to do a bit of extra free lancing work on top of my regular job. 

I have my own personal SIM which I have a contract that gives me unlimited calls. What I would like to do is get another SIM as a work number to give to clients. To keep this SIM active I just want to pay the minimum amount (I think it is 10 Euro every 6 months or something like that) so that clients phone my work SIM and not have my personal number. 

With having unlimited calls on my personal SIM I'd like to phone my clients back using my personal SIM as it costs me nothing extra but make it look like I'm phoning from my work SIM. 

Is it possible to do this? Is there an app that can control this?

I could always just phone my clients using my personal SIM and withhold my number so my number doesn't show but that's not really what I'm after. 

Does anyone know is this possible?

Thank you
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.