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Wouldn't it be EDGE only which would mean it would be slow as molasses?
 
I used to be able to tether on my T-Mobile iPhone 4 on 4.3.3, but now on iOS 5, the feature has completely disappeared. :(
 
If you JB and install TetherMe, MyWi, PdaNet or any other tethering hack it will work.
Offcourse it will be edge only.
On stock firmware you might have to enter the correct apn settings but still not sure if the tethering option will appear.
 
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