How to get iphone working with tmobile?

I have a t-mobile sim, and I am looking to buy an iphone 3g (or whatever i need) and put my sim in.
Does the iphone 3g have a sim slot?
Do I need to unlock and jailbreak to do this and is it difficult?
What OS software should I be running?
Anything else I should know about?
thanks

Yes, the iPhone 3G has a sim slot.You can upgrade to the latest iOS.Jailbreak and Unlock are two different terms but they are both usually confused. Jailbreaking allows a user to install third party applications, software, themes and removes the limitations that are on the apple device. In short it gives the user the root access to iOS whereas unlocking means the user can switch between network carriers.So, if your phone is locked with a different network, you can unlock it using the network provider or a third party unlock like Unlocking4u.com and use their permanent remote unlock service.