Will my iPhone be covered by the unlimited texting?

I would like to buy the 16 gig iphone. I currently have a contract with AT & T that expires in 4 week’s time so I will be in a position to upgrade. When I buy my iphone I have to also get the 30$ data plan and I already have an unlimited texting plan for family.
Will my iphone be covered by the unlimited texting? I have read online and people have said it might work and I think it will not!
