I wish to unlock the nokia bl-5bt it is restricted sim card

Edited to remove SHOUTING. Please turn off caps lock! Also it appears to BL-5BT so I edited that as well

That is the model number for a Lithium Battery. Please don't open up lithium batteries as they burst into flames.

https://www.google.com/search?q=NOKIA+BT-5BT+2600C-2

Your phone appears to be this

Nokia 2600 classic - Full phone specifications - GSMArena.com

https://www.gsmarena.com > nokia_2600_classic-2221

Nokia 2600 classic MORE PICTURES. Released 2008, March 73.2g, 12mm thickness. Feature phone ... Battery, Type, Removable Li-Ion 870 mAh battery (BL-5BT).

To get into the phone, the search query would be

make model tear down or 'disassembly'.

...

You can get your restriction code from your service provider or else try to get from any one of the online unlocking service provider like Mobile-Unlocker.com Here you can remove your network restriction at low cost.

You can get your restriction code from your service provider or else try to buy from any one of the online unlocking service provider like
TheUnlockSpot.com

then your mobile phone has single sim not dual sim

Hi is your phone asking for restriction code then it means your phone is locked to one network provider due to this it wont accept other network sim in it ....You can get restriction code from online sites like Onlinegsmunlock.com here they render unlock code for all mobile models ..You first check that whether they render code for your country and network provider ..If yes then pay for it and unlock your mobile ...

You can get free restriction code for Nokia DCT 2/3/4 model from www.unlocking4free.com just submit your mobile make, model, Country and network. The free restriction code will be provided.

You can get the Restriction code for Nokia Phone at here Simpleunlocking.com/nokia/rs16wp8/ and get the Free Unlocking instructions at here Mobileunlockguide.com/ unlock it step by step.

Hi, click the link:
http://europe.nokia.com/find-products/accessories/all-accessories/power/batteries/nokia-battery-bl-5b/compatibility

When you place a new or a existing SIM card from another phone provider into your mobile phone and it asks for a Security code then :-
This phone is locked to the original mobile phone provider. You need to contact this mobile provider to ask for the unlock code (security code) for this phone. You need to provide proof of ownership etc and the phone's unique IMEI number which is located inside the phone under the battery. They use this number to generate the unlock code for your phone.
They should provide you with instructions on how to enter this code into the phone.
Once you unlock the phone, then you can insert a new SIM card in this phone or sign up with another phone provider using this phone.
You could ring the phone provider and ask for the unlock security code because you are going overseas and wish to use your phone with a prepaid SIM card from another country. This maybe a free service.
The other way to get your phone unlock is to use a phone unlocking company on the Internet, they usually charge a couple of Dollars for their services. Use Google and search for "Security unlocking code” companies in your area.
You can also try these WEB site :-
http://www.mobileunlockguide.com/mobile-phone/
www.unlock-free.com/nokia-master
The IMEI number is unique the each mobile phone.
The number is printed on the label under the battery.
You can also get the IMEI number by entering this on your phone
*#06# It will then display your IMEI number and you may also get a unique global serial number. Your IMEI number should be 15 digits.

hopefully you tried 12345 if that default code does not work then try taking it to a repair center to have the code reset if they have the bb5 box.