How to use an iPhone on T-Mobile?

[JEM6]

I have researched this for a while, and have found little tidbits of information on the subject, but I have never really found a simple guide to using an iPhone on T-Mobile.
I am currently on T-Mobile and would love to use an iPhone 3GS. Where do I start? Do I need a special SIM card or can I use my current one? For service can I just use the $10 a month internet plan in addition to my call and text plan? What would be the most up-to-date way to unlock a 4.0 iOS iPhone and successfully get in working on T-Mobile?

Basically guys, I just need a starting point on how to do this. Your help would be greatly appreciated.

 

[Applejuiced]

You will need a JB and unlocked iphone or a factory unlocked.
Not all iphones can be unlocked, its depending on the bb besides the iphone 2G that can be unlocked and JB at any time.
After you get one unlocked you just stick your sim in and if you have a data plan you can enter the correct APN settings and get data. But only Edge data with Tmobile USA, 3G is not compatible.

 

[bigsexyy81]

Step 1: Jailbreak
Step 2: Unlock
Step 3: Insert SIM

Start here: http://www.iclarified.com/jailbreak/index.php

**Keep doing more searching. There are probably hundreds of articles on how to do this and most people on this board will suggest searching more.

 

[JEM6]

Thanks for the help. I will continue my research, and if you guys have any more links, it would be appreciated. So the iPhone 3gs running iOS 4.0 can be unlocked just as easily as any other iPhone? There are just so many variations I have found for different generations of the iPhone, and it can all be a bit confusing.

 

[Applejuiced]

Thanks for the help. I will continue my research, and if you guys have any more links, it would be appreciated. So the iPhone 3gs running iOS 4.0 can be unlocked just as easily as any other iPhone? There are just so many variations I have found for different generations of the iPhone, and it can all be a bit confusing.

Yes, 4.0, 4.0.1 and 4.0.2 can
If its on 4.1 already it cannot be unlocked yet.

 

[JEM6]

Yes, 4.0, 4.0.1 and 4.0.2 can
If its on 4.1 already it cannot be unlocked yet.

So if I update to 4.1 while it's unlocked, the phone would just simply no longer work?

 

[Applejuiced]

So if I update to 4.1 while it's unlocked, the phone would just simply no longer work?

It will work only with AT&T sims it will not be able to be unlocked for the time.
Unless you update to 4.1 using pwnage tool in order to preserve your unlockable baseband.

 

[eastercat]

Also, if you upgrade to 4.1 and manage to downgrade, your baseband will still stay at the updated (locked) version. What does it say in settings>general>about>modem firmware?