One thing I've always done or wished to do with my phones is www browsing in portrait mode. I mean, done with the E90 and the Sonyericsson p800, wished with the other communicators and at times with tablets.

There have been times I had to walk and keep something in one hand (including wife's hand :-) and had to find quickly something on the web, maybe an address or a phone, sometimes had to reserve a ticket for a trip or a show... Well you can imagine other uses from your own experience.

Being able to switch the browser in portrait mode - with optional page elements re-organization to fit into a narrower width - could be a bonus (not a showstopper, though).

Other apps or use cases that could enjoy an optional or switchable portrait mode:

* sms - texting apps - it happens you have to use them when one-handed
* shopping lists - when you're pushing your cart and keeping your baby quiet, hands are never enough
* maybe the calendar, at least for browsing (not editing)
* calculators, at least for the main operators + - * / and for currency conversions

After examining my symbian phone and my tablet, I can't think of other ones