link below from the X10 forum has many specific carrier settings in post 2:
Some of you seem to be missing the point here, this merely makes sure your device is performing at it's best, actual speed is largely determined by the mast.
Most ROMs have these settings by default, by removing them you are unoptimising.
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I will add "for those having problem" on the thread label.
You guys are missing the point, this is not to increase your speed if you are already at 6mbps download 2mbps upload. This is fix, not a magic.
For some people the fix did work. For me it's pretty clear when I add the fix to when I remove it. Anytime, anywhere I tested, if I remove, I go to really low (as in 1mbps download) speeds. If I add them, I get better speed.
I am currently using a "4g sim card" (I am not sure if it has anything different from a regular card) with a 4g unlimited data plan (grand-fathered) on ATT. I am currently on VA, close to DC area.