[Temporary solved]
(sorry for improper english)

Finally 2 days back iam also facing the problem **Telephony functions disabled**,this problem occurred 6 months before but not major some times solved by rebooting.But now the message Telephony functions disabled comes & not working even after reboot.iam surely know it was sim card slot probem due to loosely soldered or loose contacts on pins...ULTIMATELY IT WAS NOKIA'S DESIGN FAULT....

Because 5 years back i was used nokia 1122 model that model also this same problem,that was solved by an idea(placing a unused sim card in between battery & sim card holder for providing excess pressure to sim card holder) permanently.

So i decided to do that method by placing one unused sim card between battery & holder.But the problem occured again after 5 minutes when the keyboard opened or any shake in the phone. i decided that pesure is not enough so i placed another sim(now 2 sims in between battery & holder) by this bottom right corner of back cover slightly unclosed(not major)....

Now the problem solved iam using my n900 last two days without problem.i was opened keyboard so many times & shaked the phone hardly & changed the battery several times, now that problem not occurred(but need some long time test).iam now busy with work, after a week i will try some solderings in sim card holder with the help of my mobile technician friend & will post the result.In between who have this problem may try this method & post the result....

i mentioned nokia design problem because sim card holder is directly placed below the battery without any protective layer covered this will result heating & cooling on sim card holder,due to this method the solder or contacts may get loose or some moisture forming( we know other phones also equipped this method but the solder material or contacts pins maybe better quality than nokia & also iam not blamed all nokia models) Now a days some phones have side removable sim card holder without any direct contact with battery heat....

And iam sure my next phone will not be an nokia phone.I LOVE MY N900 FOR..
1-BETTER HARDWARE(KEYBOARD,STYLUS,IR,KICK STAND,PIXEL RATIO,LENS COVER ,32GB,FM TRANSMITTER)
2-MAEMO OS
3-*TALENTED & DEDICATED & HELPABLE COMMUNITY*

you are right about the expansion & contraction thing... dont know how Nokia handled it (alloy solder or something) coz its not a general problem regarding N900..
& if the door is not closing the packing is more than enough... try setting a cardboard or multi folded tissue paper,keep it exact size as the Sim-bed for even pressure & correct closing of back - cover

GODbless

see samsung s3 sim card holder safely away from battery to avoid any heat disturbances.As i mentioned some(now many) phones following this safety procedure.i noticed so many guys have this failure on their phones,this will permanently cure by any soldering technique in the sim card slo only.Hardware expert idea from nokia is appreciated.

Nokia did it in back in 2004 with 7710, its just they didn't applied it in N900...




the sim slot we see at the top of iPhone was originally introduced in Nokia 7650 back in 2002



Nokia has done many things in very early years that are now followed by the Technology

Yes,my older nokia phones also equipped with good hardware technology but now a day's.......?

Anyway last 5 days my n900 working very good with this technique(now also) without any single network problem.Now iam thinking can i do any solder on sim card slot? or permanently following this technique?

I LOVE MY N900 FOREVER...

I noticed that there are 7 pins located at the sim card connection location. 6 are used to make contact with the sim card and 1 is probably used to check if the sim card slot is locked correctly. If you bend up the 6 pins, also make sure you bend up the 7th very tiny pin. I am not saying it really solves the problem, but maybe some might be able to solve a problem caused by this very small 7th pin on the side of the sim card slot.

I have not had this problem (yet?). But AFAIK the problem is not whether the SIM card makes good contact or not. You don't need a SIM card to make an emergency call.

The problem is (apparently) that the GSM CHIP loses contact.

@reinob Most phones do indeed not need a sim card to make an emergency call. I think the N900 however does need it.