I am looking a developer for a message application, which should be very much like WhatsApp or Signal and run on Android/ iOS. Since I don't have exact budget I would like to hear from you with offers (preferably fixed) and also ideas of development in terms of what technology components you would use. The application should provide security for users and scale up to millions of users. I also would like you to provide ideas of what would be the monthly maintenance fees to start with and then when the user amount grows. ...and yes, money matters. Thank you.