Will updating the iOS remove the unlock?

I have the iPhone 4 on tmobile and want to get ios 6. And I was wondering if my sim card will still work after the update?

Yes it will remove the unlock.

Yes Updating IPhone 4 will remove the Unlock. You need to Unlock it again… It's for only I-phone.Other Branded Phones once Unlocked It's unlocked for ever. They won't get locked again. You need to specify the current country of T-Mobile it's locked now. Then get Remote unlocking service at http://www.mobileunlocksolutions.com/apple-iphone-4/rs1wp9/ and unlock it from network lock. Here you can get Netherlands and United Kingdom(UK) T-mobile network Unlocking service.