You'll have to explain in more detail, but It's not out of the question. Considering that (especially in non-BB phones, which don't have PINs) you would need to talk directly to the phone to get it's GPS coordinates anyway, you'd almost have to know it's number to find it.
Now, I seriously doubt if I gave him my number and then he tried to locate me (without adjusting anything on my end) it wouldn't do it. I'd have to have a program that would send my GPS coordinates to him.
The app in question only gives the iPhone users location. It displays your cell number and since you are standing within viewing distance of the iPhone it "locates" you.
