I want to send an alert from iPhone to Arduino (Using modules like HD-505,etc.) When the iPhone(Rings) gets a call.How can I achieve that? I searched on the net but I couldn't find anything.
ANY HELP IS APPRECIATED 
If you do a Google search, you will find several examples of controlling Arduino's (and servos for instance) over Bluetooth from a Smartphone.
So I guess what you need is an app on the phone that sends a message over Bluetooth when the phone rings.
More of a iPhone problem than an Arduino one I guess.