Sims card for nextel phone?

I tryed to change my sim card for my cousin in my nextel phone from her cingular phone to get her numbers so she can call her mom,it wouldnt gp through so we tryed to change it back and it needs an 8 digit special code,I cant let my parents know,How do i fix it?????PLease help!!!!!!!!!!Sims card for nextel phone?
Sorry, but if it hasn't corrected itself, then you are going to have to tell them. They'll have to get a hold of Nextel to get help. Just because a phone uses a sim card, it doesn't mean it's compatible with any sim card or provider. Nextel's phones and network are iDEN, while Cingular/AT%26amp;T's phones and network are GSM. They are not compatible technologies. Next time, don't try to swap sim cards if you aren't sure of the type of network the provider uses.