Will iPhone 3GS Unlock work with T-Mobile?

It should work, that said if you live in a refarmed spectrum area (T-Mobile is using 1700 MHz 3G and 4G but is upgrading most of their towers to support the iPhone).

http://www.airportal.de should give you an unofficial reading if you're covered.

Yes, if its IMEI unlocked then it will work fine with tmobile.

Chiuy said:

The phone was originally ATT and I unlocked it then updated to the latest software version 6.0.1(?)
Will the phone work with T-Mobile? I unlocked it by purchasing a IMEI unlock code on eBay.

Do I need to jailbreak it?

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You do no need to jailbreak it if it is unlocked. You can use it on T-Mobile if you have a T-mobile sim card. If your area has not been updated, you will get Edge data speeds until then.

Applejuiced said:

Yes, if its IMEI unlocked then it will work fine with tmobile.

Click to expand...

Yes (I just checked for my old 3GS).