Google hangouts. What these little icons mean?

[Shurup]

Question obviously for those of you using the Google hangouts. On android, because I don't know if it looks the same on other platforms.

You know there on a bottom of the screen, there's a little bubble showing where the other person finished reading in the conversation.

If you click on it, it will say the the person has read up to here. Sometimes there's a small icon below it that looks like a mobile phone (as on a screenshot), and sometimes there's another icon that looks like the old fashioned phone receiver.

So my question is, what are those little icons mean? I'm guessing the small mobile icon means that the other person is doing something on their phone, and the small phone receiver means they are talking on a phone?

Anyone has any other guesses?

[Shurup]

Attachment.