What Is The Difference Between An Unlocked Iphone 3g And A Regular Iphone 3g

I am sure you all know about the iPhone 3G finally being unlocked. I am looking to buy one and I want to use my T-Mobile sim card that carries the $29.99 300 min and UNL. N&W Plan. If I use that sim card, will I still get all the features like GPS, internet and texting? Thanks!