The content, i can see it but i cannot acces it ( i can see the files on the card, but cannot open them).
I have tryed this with the default file manager and filebox.
And yes, i think it only unmount /dev/mmcblk1p1, but that is how it should be

To be completely honest, for (really great!) SD card mod like yours, I would preffer to have a magnet glued to N900's inside case, close to sensor and use a pair of scripts for completely safe mounting and unmounting of everything SD (and for those that need it, create a fancy shortcuts or QB widget for it).

This kickstand thing seems too random for me, I wouldn't be sure that it's reliable enough (aka: it won't open accidentally). In fact, I'm using exactly this - glued magnet - that allow me to remove cover whenever I want and pair of scripts to shuffle SD card mounting and swap between SD/eMMC, when need arise.

Frankly, using such setup I don't see removing cover to access SD slot as any hassle, but, our needs may be different, and your way of executing this mod is very professional (from outside, it looks like it was designed this way all the way from factory), so kudos for that

/Estel

// Edit
What would see *very* useful, would be a way like that to shuffle SIM cards, without removing battery. Won't happen though, I guess.

Well, the kickstand stays quite good, i doubt it would accidentally open.
I need to fast remove the card, so the magnet does the job really good, when i remove the magnet the card is almost instantly gone.
I insert/remove the card very often, becase i need to copy or edit files for raspberry pi, and windows doesen't recognize linux partitions.
About the sim card slot, it is verry easy to do, but i simply cannot find any space left for a second sim slot, but the idea is simple: you need to solder to the sim slot pins, some thin wires, cross them above the battery, and solder them to a second sim slot above the battery. When you want to change sim simply put the phone on offline mode, change the card , put the phone back on normal mode (this works in theory, but i did not tested). This has been discussed on this thread before, i said i would do it, but unfortunately i have no time (and space left in the phone).

I vaguely remember someone confirming, that offline mode isn't enough to facilitate SIM card switching, and modem goes apeshit if new sim card is inserted during device runtime (doesn't apply to dual-sim adapters that use so-called 007 mode - see:
http://talk.maemo.org/showthread.php?t=85722)

As we, obviously, can't modify modem's firmware, I'm not sure if it's fixable. Hardware part of this mod is quite easy to do, of course.

/Estel

How could anyone have tested this?
As changing SIM always had the need for swapping battery!

In general I do not see why it should not work, as also those adaptors do nothing else than switching circuit form one SiM to the other (but okay maybe some power on initialising going on?).

If you like to try do a simple
This will cleanup (a bit unnicely but as first shot), then we can have a look at phonet-helper script ...

By providing ~4V to battery pins and connecting BMI pin to ground one via 100 kOhm resistor

Frankly, I have no idea, but I would like very much to test it! When I'll set up my no-battery hack again, I'll borrow from your expertise on phone stack and maybe we will find a stable way for such hypothetical mod.

/Estel

OK. Time to clear this sim swap mistery. A few days ago i dropped the n900 on the concrete and some parts wouldn't work anymore so i had to open the phone to repair it and decided to test the sim swap.
Sorry no camera at hand to take pictures
So i soldered some wires from the sim slot of n900 to a sim slot of a nokia 3310.
1 Started the phone with a vodafone sim card - ok
2 Put the phone in offline mode, remove tyhe vodafone card and insert an orange sim card
3 Put the phone back in normal mode - a message pop up on the screen displaying "GSM: orange", but on the operator logo on the screen the text was still showing vodafone, but i could call and be called on the orange sim.
4 Decided to remove the sim without puting the phone in offline mode - It worked! in a few seconds after the sim is changed a message popped showing the network of the sim i puted on. however the operator logo was still showing vodafone, no matter the operator sim, but that is not a big deal since the phone is on the network of the inserted sim
5 Started up the phone without a sim card, and inserted the sim after, in this case i could not get the phone to acces sim
6 i decided to do mmore, since it is a gap of a few seconds from when you remove the sim and the phone realising it has no sim, i wanted to check something:
i removed the sim card during a phone call and guess what? The phone call continued without the sim!!! i couldn't belive it. My first thought were wow i fond a vulnerability to make free phone calls!!!
Unfortunately it didn't worked that way: I put a cosmote sim on n900 and called miself on the orange sim. Before answering i removed the cosmote sim form n900 and answered. it worked, but when i check the credit on cosmote i saw i was chrged, even if cosmote sim was no longer in the phone when i answered.
However the conclusion is that sim swap is possible and very easy, you don't even have to tur gsm off when changing the sims. The only "problem" is that the operator logo of the sim you started up the phone remains there, no matter the sim. ( ithink that can be fixed by refreshing the hildon desktop, but i didn't bothered to do that).
About the drop that make me open the phone, it was a nasty one. The battery jumped out of the phone almost a meter away and the back cover received a crack under the solar panel(but thanks to it is not visible).
My first thought were that the gsm chip or emmc got damaged by mechanical shock, but to my surprise, the worked, bluetooth and wifi also worked. I thought everything was ok. But later on i discovered that flashlight wouldn't work anymore, neither the main camera, neither the secondary camera and as a bonus gps was also dead.
The gps repair was easy all i had to do was to heat with hot air the gps chip for a few second, and the gps was back to life.
The main camera simply showed a black screen, the secondary cam (using the mirror app) showed something like "gstreamer error", and flashlight app was dead. All this problems camed from the main camera module that got some internal damage from the shock. The solution was changing the main camera module.
I always saw that nokia n97 takes silghtly bettet pictures than n900, and in every review i saw on the internet when comparing the camera of n900 vs 97, the n97 wins.
So i had an n97 lying around and decided to put its camera module on the n900.
At first sight you will think they are very different, since the n97 camera module has a ribbon cable that connect to the motherboard, and the n900 module has just some pins.
But if you peel off that ribbon cable of n97 cam module, you'll discover the same pins. So i did, placed the n97 cam in n900 and it worked!
My n900 now takes better pictures than before with the new module. Also the flashlight and secondary camera went back to life after module replacement.
With this setup i wanted to do more, so i opened my nokia n86 in the hope i will be able to do the same and to have an 8mpx camera on n900. Unfortunately the n86 cam module is way bigger than n900/n97 cam module so it wouldn't fit in there .
However i should have tested if the pins are the same, maybe with some wires soldered it would work but that will be tested next time .

swapping SIM without applying proper procedure is as critical as removing uSD without unmounting and powering down the adapter. You later or sooner will damage your SIM by doing it, the latest when you remove it during a page-erase of the flash storage.
Of course exactly like for any flash memory card (and any storage in general, no matter if HDD, floppy, CD, any cards...) the system has buffers that are not immediately flushed when dirty. Those buffers a) keep info that is not available anymore when card gets removed (see "still can see dir structure of uSD but not open it") and worse b) the dir metainfo may not be consistent, so you at very least see filesystem corruption from removing either uSD or SIM without prior sync. And removing power while flash is written can destroy the storage even physically, definitely will destroy it on low level management metainfo which also often is not recoverable by any means.
Sure swapping of SIM usually works, since the SIM usually is inactive and powered down, even when not sync'ed. But figure you swap the SIM while it's powered down and then the system powers it up again and syncs data in dirty buffers from 'old' SIM onto 'new' SIM. DOOM :-/
There's a reason why systems that allow SIM hotswap have a mandatory SIM-card-detect switch that tells modem about "pending" SIM removal. It's NOT a measure to prevent fraud, that's a silly and naive assumption. It's there to avoid damage done to cards.

bottom line:
DO NOT HOTSWAP SIM OR uSD CARDS! IT WILL DESTROY YOUR CARD.

/j

@ryu1,
Would you mind another experiment with swapping SIM cards? I would like to know what happens with the SIM card PINs. Does the phone ask for a new PIN when the card is replaced? If the two PINs are different, does it accept the old or the new one? If it does not ask for a PIN, can it make and receive calls with the new SIM?

@ryu1
Thanks for testing procedure.
About operator icon/name you are right, I did not find any other solution than killing hildon-home.

@joerg
Thanks for explanation !
Would this N97 camera module experience a possible enhancement for Neo900?

@pichlo
May I guess what happens?
If SIM do not have PIN request the swapping takes place immediately without any necessary interactions.
If a SIM has a PIN request just nothing will happen. No swapping no nothing until you restart csd (either by killall csd or phonet down/up).