It says insrert sim card, or to view a demo of this phone first, press Demo. whilst there is a sim in it

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

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

Is this a new phone? If so check that you've inserted the SIM correctly and it's not SIMlocked to another network

If it's worked before remove the SIM and GENTLY clean the contacts on the phone and the SIM with a pencil eraser.

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

the only reason it says demo mode is because you dont have a sim card in it

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?