Well, one workaround i've found after posting, is to look up the contact in the contacts list > dial it > end call > go to call history > long press and there I have 'copy number'. It's silly but it works. And it shows in the reminder as a link that I can press, it's pretty much what I was looking for.
Before I used to open the contact > edit > long press on the number > select all > copy. It was even more cumbersome. And I'm pretty sure that before upgrading to 2.3.6 gingerbread there was an option to long press > copy number directly on the contact list but it's missing now. Has anyone had the same experience?