Ok, sounds bad man. Have you tried calling in 3g mode at someplace with great 3g signal?

Well the 3g is the problem i think... After with more testing ive come to the conclusion that

the 3g part might be the problem.. It seems it wont work well/get a signal in "dual mode" because it reaches for 3g the most.. and the Single 3g option forget about it it takes pretty much forever to get a signal and then some time later to acutualy work properly (so i can make and recive phone calls)

on the other part GSM/2.5g seems to work normally. for the most part of my testing today. If i leave it on 2.5g i can recive and make call instantly as usual.

So what should i do? there is defenitly a problem with the phone as it was never like this before. it worked fine like a normal phone should. So what are my options? i still have my warrently since i bought it in november.

Send it in asap and hope they fix it? and now how would i describe my problem? i dont think the people reparing would have patience to test this problem out..

or do i keep playing with it and see for a coulpe of days and report back?
does anyone have a solution/

I had a very similar issue mate. Mine was the opposite. 3G would work fine but if it switched to GSM it would drop the call. GSM just stopped working. It would even show the no sim symbol when it went to 2G. Then it started having power issues and just crashing when it tried 2G. I sent it back and they replaced it with a new N900 right away. Sounds like you have the same problem but in reverse. Send it back.

I havent seen the no sim icon yet but the isuuse you had does sound similar to mine.

oh wow, that sucks .. i'am no fan of sending it back , i breifly did read the instructions where it says to send only the phone without back cover and charger and sim and etc.. is this correct? and the explaintion how exactly should i explain it to them? and what about the pricing it says request signature/insurance/tracking and everything how much is it going to cost me?

Just one question, have you tried repeating your tests on different locations? Just to make sure its not a problem with the local network.

Well i did take it outside couple of times and noticed it lost signal and wouldnt bring anyhting back while on "dual" i had to manually switch to gsm/2.5g to bring back the singal

but the werid thing is its functioning "normally" again so it seems. but i have no idea when it will go off again.

any suggestion guys? does anyone know how much it would cost to send it in?

Smells rather like a dodgy SIM to me.

Try this - grab yourself another phone and pop the sim from the N900 in it. See if you have similar problem.

Also, pop the SIM from the other phone inside the N900 and see if the issues continue.

If the N900 works find with the other SIM then get onto your SP / NP and ask for a replacement SIM.

Where are you located? I've seen some T-mobile network instability lately in Metro NYC as they upgrade the network. Network issues seems like a plausible culprit.

I ran into a somewhat similar issue today where my n900 could not connect to T-mobile Internet, and would not receive calls despite the usual signal strength. A simple reboot resolved the issue for me.

I will test the sim thoery with my brothers t-mobile sim, hes on the n97 mini and my sis in law has the iphone i will try both..

i am located in farmingdale,ny.. i am not sure if i should just wait or send it in.. it seems to be working fine again. it could have been just t-mobile for the past few days but i did try many reboots/flashes/removing and placing sim again. should i try rice? lol

i had exactly the same problem with you for five days before a week and i made exactly the same actions,thaughts as you do but everything went back to normal one day so i supposed that was the network (t mobile) and not the phone so my advice to you is relax and leave some days to passing and am sure that all gonna be right and back to normal soon.T mob make upgrades to the network so it's expected i think....
sorry for my poor english but am 4 months only in the states.