Will my iPhone 4s still be unlocked for T-Mobile if I update to ios 7?

A few weeks ago I got an Iphone 4s. I payed 30 dollars for it to be unlocked to T-Mobile.

I realized that ios 7 will be releasing this fall and I fell in love with it, but if I do update to Ios 7, will my sim card for T-mobile on my unlocked phone work or will it be locked and unable to use t-mobile.

If it came factory unlocked, it should still be unlocked.
If it wasn't unlocked by the factory, the lock might reset.