How come when i put my at&t simcard in my t-mobile blakberry it says sim card not valid?

Question

i want to use my sim card in my t-mobile phone and it odn tlet me so can anyone help me! thnx =] add me if u want u to answer me [e-mail] or [e-mail]

Answer 1

You need to unlock the phone.  It sounds like it's locked to the t-mobile network.  You can do it for $20 here: http://www.gsmunlocklabs.com/t-mobile-im...

Answer 2

Phones these days are manufactured to work for the company they are selling it from. For example your blackberry is from T-mobile, therefore it will only work with T-mobile sim card. But if you want to put your T-mobile sim card with a phone you bought from T-mobile company it will work; same way with At&t and other phone companies.