Hi,
I've worked on several Arduino based projects, including a quadrotor, and have worked with Bluetooth modules as well, when I was making the controller of the above said quadrotor.
I think your request is fairly straightforward, and I'd love to discuss it further with you.
My proposal to accomplish this is simple: it will be always discoverable, and should your iPhone come within range of it, your iPhone can send it a message to activate it. On activation, the servo routine will be performed.
I look forward to hearing from you.
Regards,
Chaitanya.