I just bought an android phone and the previous owner of the number had an iphone and imessage wont work, how do I fix that?

I just bought an android phone and the previous owner of the number had an iphone and imessage wont work, how do I fix that?

I recently bought a Samsung Galaxy S4, and my wife has an iphone. We found out that imessage wont come through from her. After we went to the AT&T helpdesk they said that she could turn off imessage on her phone and that I would get texts on my S4. But then so would everyone else who has an iphone. That won't work for everyone in my company that has an iphone. So what I am wondering is- since I recently got this phone, should I get a new number? Or should I contact ATT or contact Apple to try and get this number de-activated? I'm thinking I'll never get into the icloud account that this number is attached to, but maybe someone has some advice on that?

I just sincerely want imessage to work on this phone and I'm willing to take the steps to do that.

Please help