I use Chat ACS Titanium http://cloud.appcelerator.com/docs/api/v1/chats/create in my app. I've need to know if there are people of my contacts book that have my app installed (like whatsapp o viber). Is possible?
You could get all the email addresses or phone numbers or similar from the contacts book, then run a query to find all the matching users (hint: you'd use email: { $in: [ 'all', 'the', 'emails' ] }).