Can you put an at&t sim card in an tmobile phone?

I have an lg optimus.I heard you can do this but, you need an unlock code.does anyone know where I can get the code...im getting another at&t phone for xmas[samsung captivate],cusz mines broke.so as of now I have to use another number & I dont like that...so please help me out if ya can!








Thanks in advance!

I suggest you can approach unBBlock.com and specify the country,locked network of LG Optimus.Based on the availability you can get the permanent unlock service along with free instructions.