The "Online Status" for iOS and Android users:
When two people are in a 1-on-1 chat and one person puts the app in the background, their status will appear as "Away" to the other person.
However, if you miss a call, status behavior differs between iOS and Android.
On iOS devices: your status will update to "Last seen now."
On Android devices: it will change to "Away".
For Android users, if you play a radio station or MP3 and then put the app in the background, your status will still appear as "Online" to others.