you would need a phone that has dual sim slots and can handle 2 numbers. There is something for the iPhone 4 that will allow you to use two sims, but it looks like you have to reboot the phone to use it: Amazon.com: Dualsim Adapter for iPhone 4: Cell Phones & Accessories

Cell phone with 2 numbers to make/receive calls in and out. Is this possible?

If I have a company phone (iphone) and a personal phone number, is there a way I can attach my personal number to my company phone?

I would like to receive calls and be able to make calls using my personal number.