How is maintaining presence useless on mobile? I like Google Talk on android ten times better then just plain sms for this very reason. Being able to know whether your friends have service, and then being able to know whether they are actively paying attention to their phones (online/away), is crazy useful when trying to communicate.
Because there's a single thing that makes presence useful, which is the device going off or to sleep, y'know, like a desktop computer in the nineties. There aren't many people who maintain their availability by hand, as that's just a pain.
A cell phone is always on, so depending on the solution, I'm either always "online," or always "away" with some single blips of "online". Me being "online" doesn't mean I'm really paying any attention, I just took out the phone for a second while my friend was in the toilet, or anything, and now I'm gone, but will still appear as green for some time.
What's App and iMessage solves this by replacing online with read receipts, and in case of WA, "last seen online" data. Much less pretense makes it way more informative.
What he probably meant is: You don't want your mobile to be notified about presence unless you open the client and look at your roster. Or if you set a trigger to be notified if someones presence reaches a certain state. When you control the server side both is possible with XMPP. You could use privacy lists XEP-0016 for that. You'd just have to make sure that the server sends the last presence when you enable presence notification after you disabled it while the client was not in the foreground.
