One of the three visible teeth one seems to be broken off completely. A SIM card - which works with N900 - doesn't work with N950: crossed SIM card icon is shown in statusbar. Nokia N950 has Nemo installed as Single-boot, no Harmattan.
Would it be possible to repair it somehow? Space is not an issue: I can ask the provider to send me a micro-SIM or nano-SIM instead of the current mini-SIM.
However, it's preferred to not disassemble the device. I have bad history with non-standard screws.
Asking for help. Thanks in advance.

actually, they are standard Torx screws. Just get a cheap torx screwdriver and open it up.

if you put in mini/nano sim, it'll be stuck forever!!! and could cause even more damage when trying to remove it

Well, I will have to look around for a torx screwdriver. If it happened a week ago, it would have been an easier task; but now, the closest hardware store has already closed.
The fact is, I have completely destroyed about four Philips screws when using a '+' screwdriver, and I am wary of even touching six-ended-star-screws.
When will a manufacturer produce a phone with multi-use standard screws and make its profit on selling spare parts to people - both do-it-for-money-for-cautious-user professionals and do-it-yourself-at-home hobbyists - instead of considering each phone a separate product incompatible with others?

Thank you for the warning. Yes, it would be nearly impossible to get such a small nano-SIM card out of this slot if it got stuck in it. I was asking about it because it is rumoured to be thinner, and if some soldering changed the slot so that standard SIM would no longer fit into it, the nano-SIM would have still had the chance.

These slots-ports are quite fragile. I am fortunate that micro-USB cable of N900 is wearing out, and not micro-USB port of N900. There was a moment today when I was afraid that the port itself no longer works, but now it's fine and merry.

Best wishes.
_________________
Per aspera ad astra...

Another work around for you:

Solder a little (thin/small) hardwire to your simcard, so when you insert the simcard, it will make contact to the broken place.. who knows if you make it good, it should work without destroying your phone :P

Another image.
How do I check whether the other three teeth (far away from the opening) are fine?
Could this damage be caused by pushing memory card into SIM card slot?
Afraid of soldering such small parts. Does the material of the wire play any role? Copper or whatever...
What's the chance of finding such small tooth on the floor?

I really don't know.
i think it's worth the shot, since it couldn't damage your phone
as long as it's a hard wire/copper, it would be fine i guess.

or just bring it to your local repair guys :P

U can use a thin copper plate fold it then solder it to the board.

Dont try to place some solder alloy to make contact as it looses connectivty ofen

moreover do it carefully as if it conects diff region it will render sim as well as the sim ic shorted
as hiteb said go to some repair guys they will handle it with ease

do not try it

Waiting for more opinions...
Looking around for the closest repair guys who would be able to look at my photograph of the SIM port, or the device itself, and give their price quote.
Still hoping for DIY solution - but unlikely, given my tools and skills.
Thank you. Best wishes.

it seems it is better to not try diy as your post says
and would you please add some photographs of the board , simslot please