have a 3G 16gb iphone and I want to jailbreak and unlock it so that I can use it for T-mobile carrier. The version of the firmware is 3.1 could someone help me out how to jailbreak my Iphone so that I will be able to use for T-mobile service. Thanks for your kind help...

Why don't you ask AT&T. They can help you on this.

They won't because I am not using their service.

the firmware 3.1 hasn't been unlocked or jailbroken yet so you might have to wait a few more days. what you might wanna do is downgrade it to 3.0 and unlock and jailbreak it. google redsnow  and unlkand download it. it has some info dat comes with it and is very helpful.

try this website
http://blog.iphone-dev.org/post/126908912/redsn0w-in-june

this is the dev team's website they are the ones who put out programmes like redsnow,ultrasnow,pawnagetool and quickpawn.....

and 3.1 has been unlocked by them but it is a complicated process and u might brick ur phone in the process

so better stick to the firmware version 3.0 and unlock it

they have detailed instructions and firmwares in the website mentioned above
hope this helps

check the modem firmware is it 4.26.08 or higher ...

try this
http://www.poorlad.com/iCommunity/

You Just need to unlock the your IPHONE to use in T Mobile.You can borrow ATT sim card & Call ATT or go to their store and ask em to Unlock ,saying you are going away frm country..stores might charge you few dollars though. Dont worry about Jail Breaking unless you want to run your own unofficial APPS not recognized by apple.

here's a link for to jailbreak, i am also trying to jailbreak & unlock my 3G, Please do share a link if you get any for Unlocking

It locked to which Country's Network ? You need to specify that!!!
You  can get the remote I-phone 3G unlock from here
Simpleunlocking and get the Phone Jail breaked at here jailbreak-my-iphone.com then after Unlock it you can use with any GSM Network Sim like T-Mobile.