I don't have a SIM in my FP2 yet to try reproducing this myself and also I'm not exactly sure what we're talking about here? Can't you edit the phone number for the owner id or can't you edit the number displayed for your own sim?
In the first case I'd say it's a bug if it's reproducible, in the second case it would be a feature request.
@Lidwien If you consider this a bug it's ok to add it to the list of bugs but the way to do that would be:
- move this thread to the bugs category
- edit the list and add a link to this thread