I have a new samsung mobile phone and i insert sim card but diplaying message is invalid sim card what is the problem?

When do you get this message? Are you getting this message on inserting any new SIM card to your phone? I think you mobile phone has been locked to some specific network. You need to unlock it to make work on all SIM card. You can unlock your mobile phone safer and easier using unlock code.
If you are having a Blackberry model mobile phone, you can visit
UnBBLock.com to get the unlock code.
If you have any other mobile phone model, You can visit Mobile-Unlocker.com to get the unlock code. Good luck.

Hi if your samsung SGH-E900 mobile is displaying sim invalid message once you insert your sim in it then it mean your phone is locked to some other network provider due to this you can't use other network sim until you unlock it ....You can easily unlock it using sites like SimpleUnlocking.com they are providing unlock code for all mobile models at reliable cost ....

What is your problem with your Sim card? Is your phone shows the "No Sim" or "Insert Sim" or "Sim Rejected" or "Invalid Sim" error? If it is so i am here to help you. If your Samsung shows the "No Sim" or "Insert Sim" error then remove your Sim from your mobile and place it again correctly. If your mobile shows the error message "Invalid Sim" or "Sim Rejected" the your phone is locked to a particular network. To fix this problem you need to unlock it. Use unlock code to unlock your Samsung B5310. To get the code you have to submit network provider, country and IMEI number of the mobile. Make sure yourself whether you have knew the network provider to which your mobile is locked, country to which the locked network belongs to and IMEI number of your mobile. If not you can find the IMEI number in two ways:
1)Go to Options>status
2)Find IMEI on the back of your mobile, behind the battery.
3)Type *#06# and press call button. It will display your IMEI number.
You can find the network provider to which your mobile is currently locked by switch off your mobile and switch on it again. A logo of the locked network will get displayed on your mobile screen. After knew all these get the code from the site Theunlockarena.com ,by submitting these to them. Unlock it yourself using unlocking instructions which is given in the site itself.

What is your problem with your Sim card? Is your Samsung phone shows the "No Sim" or "Insert Sim" or "Sim Rejected" or "Invalid Sim" error? If it is so i am here to help you. If your Samsung shows the "No Sim" or "Insert Sim" error then remove your Sim from your mobile and place it again correctly. If your mobile shows the error message "Invalid Sim" or "Sim Rejected" the your phone is locked to a particular network. To fix this problem you need to unlock it. Use unlock code to unlock your Samsung . To get the code you have to submit network provider, country and IMEI number of the mobile. Make sure yourself whether you have knew the network provider to which your mobile is locked, country to which the locked network belongs to and IMEI number of your mobile. If not you can find the IMEI number in two ways:
1)Go to Options>status
2)Find IMEI on the back of your mobile, behind the battery.
3)Type *#06# and press call button. It will display your IMEI number.
You can find the network provider to which your mobile is currently locked by switch off your mobile and switch on it again. A logo of the locked network will get displayed on your mobile screen. After knew all these get the code from the site Wickedunlock.com ,by submitting these to them. Unlock it yourself using unlocking instructions which is given in the site itself.

What is your problem with your Sim card? Is your phone shows the "No Sim" or "Insert Sim" or "Sim Rejected" or "Invalid Sim" error? If it is so i am here to help you. If your Samsung shows the "No Sim" or "Insert Sim" error then remove your Sim from your mobile and place it again correctly. If your mobile shows the error message "Invalid Sim" or "Sim Rejected" the your phone is locked to a particular network. To fix this problem you need to unlock it. Use unlock code to unlock your Samsung . To get the code you have to submit network provider, country and IMEI number of the mobile. Make sure yourself whether you have knew the network provider to which your mobile is locked, country to which the locked network belongs to and IMEI number of your mobile. If not you can find the IMEI number in two ways:
1)Go to Options>status
2)Find IMEI on the back of your mobile, behind the battery.
3)Type *#06# and press call button. It will display your IMEI number.
You can find the network provider to which your mobile is currently locked by switch off your mobile and switch on it again. A logo of the locked network will get displayed on your mobile screen. After knew all these get the code from the site Wickedunlock.com ,by submitting these to them. Unlock it yourself using unlocking instructions which is given in the site itself.

I think your phone is locked to a particular network other than AT&T....so only when you insert AT&T sim you are getting the error message "Sim card invalid"...What is your mobile model? You can get the unique unlock codes for your mobile from unBBlock.com (especially for Blackberry mobile models) at low cost with free unlock instructions.

What is your mobile phone brand and model?If you mobile phone displays the message invalid sim card while inserting other network sim card,its locked to network...You have to unlock it...Visit the site
Mobileunlocksolutions.com/supported-phones/rs1wp7/ get the Unlock code and unlock it easily.After Unlock it will accept any GSM Network sim card.

kindly change the frequency of the mobile.

Easy way to Unlock The Mobile.U can Use the site http://www.mobileunlockguide.com/ First For the Mobile Unlocking Process