On my screen it says insert sim,or view demo of the phone this phone first,press demo.my sim card is working but nothing happening on phone.

You need a SIM card to make the phone work. If one is already installed it has failed or the card is not installed correctly.

Sim contacts may be dirty, either on the card or phone.
remove sim card and GENTLY rub a pencil eraser on the contacts to clean, then test. If you can access the contacts on the phone, do likewise. If not, then you'll have to use an Ether based cleaner, Like electrical parts spray ( available from your local auto parts store) .
be careful not to spray too much into the phone, as once the spray gets inside it takes longer to evaporate. You can counter the time by using compressed air to speed drying of the phone interior without taking it apart.
Hope this helps!!

My sony ericsson j20i mobile showing "insert sim card or to view the demo of this phone first view demo" at first i thought it was simlock by that network after checking with omnius for SE software it shows the phone is not locked by the network
wat does it mean? why its not detectecing pls help me
my mail id is [email protected]

you can get unlocking instructions here http://www.mobileunlockguide.com/sony-ericsson-t715a

Make sure the sim card is inserted in there correctly and if its still not reading the sim card it might have a Bad sim card reader

Hi

This is happening because when the Sim card is not inserted you cannot access the menu of the phone some nokia phones(including yours) are built that way.

Some nokia phones do not need a sim card for you to access the phone menu (e.g 5130,5230), while you can only view the demo of some nokia phones (e.g 1208, 1600) without a sim card

Hello

To avoid this kind of problem from recurring;

Make sure your Sim card is properly inserted

Make sure you avoid hitting the phone on objects and also avoid dropping the phone because this can make the Sim card shift out of place

Goodluck

http://www.megaupload.com/?d=QKFIVMIP
go to this website and then download the software....its an unlocking software.....hope it helps.....dnt forget to vote for my answers

i got a sony ericson k550i the display reads insert sim or view demo but simcard is in the phone. Why did this happen

Hey i'm having the same problem with mine, u prob got it sorted by now but i found that it is because my sim card is so old, tested it with my friends brand new sim card and works fine, 
did you solve the problem?