IM in your pocket?

So I am reading "Smartmobs", the book not the web site, and at the same time have become aware of more people using IM on mobile devices like phones. It's a fascinating phenomenon.

I notice for me, that when a message goes to a mobile device, accidentally or not, I feel like I just intruded. I don't feel the same way if the same message had went to a PC IM client. When I send an IM read on a PC client, it seems as informal as writing a note and leaving it on someone's chair. When it goes to a mobile device it feels more like leaving a note in someone's pocket or their purse. My message just wasn't that important. It didn't have to wing its way across the internet and then across the cell phone infrastructure. I didn't need it taking up precious memory embedded on a hand held device anywhere.

I'm not sure that this reaction is normal. Perhaps it will fade in time after IM with mobile devices get more mainstream like it is in other parts of the world.