Is there an iPhone app that tells me if my contacts are iPhone users?

Certain apps I have only allow me to use them with other iPhone users. I don’t know which of my contacts are iPhone users, so is there an app that would let me identify the iPhone users?
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AT&T Deal to Let Users Unlock Phones, But Not iPhone

AT&T Deal to Let Users Unlock Phones, But Not iPhone
AT&T has reached a class-action settlement that will let customers unlock phones tied to the carrier – though that does not include Apple’s iPhone, with which AT&T has an exclusive contract.
Read more on PC Magazine

iPhone users reporting early upgrade offers

iPhone users reporting early upgrade offers
Did you jump on the iPhone 3GS right when it came out? If so, you may not have to wait the usual full two years to qualify for discounted pricing on the next-generation model. The iPhone 4G has been widely rumored to launch on June 21 or thereabouts, to coincide [...]

The IPhone Aids The Shoppers Receive The Message

It used to be that cell phones were used just for making calls, but that isn’t the case anymore. When people purchase a cell phone, they want to not only be able to talk on the phone to their friends, they also want to be able to talk to their friends with chat as well.
One [...]