Thanks for the info guys, it makes more sense now 
Another thing, doesn't two ticks indicate the device has received the message? My friends say they only see one tick and the second tick comes once i open the app itself. On android it used to send 2 ticks whenever the device received the message regardless of if the app was open or not, or is this just the way it works on iPhone?

Another thing, doesn't two ticks indicate the device has received the message? My friends say they only see one tick and the second tick comes once i open the app itself. On android it used to send 2 ticks whenever the device received the message regardless of if the app was open or not, or is this just the way it works on iPhone?