Helmuth, I know about your Brainstorm and have voted on this but as you know Nokia WONTFIX it

I thought may be Nokia will change buttons position at least?
And add this option as a checkbox in, for example,
"Settings -> Phone -> User interface -> Put Reject button on the top in portrait mode during incoming call"
AND/OR
"Settings -> Phone -> User interface -> Split Reject and Answer buttons vertically in portrait mode during incoming call"

IMHO, it's a little bit easy to rearrange Answer and Reject buttons than add swipe options and Nokia will compromise to change UI for incoming call, "split/rearrange buttons".