I don't know for sure on the Note 3, but on my Note 1 with CM10.2 (now CM11) I am able to tether as much as I want on a non-tethering prepaid plan. When I try the same thing on my Note 3 (using N9005 ROM so no T-Mo modified tether menu) it successfully connects the laptop but only ever goes to the T-Mobile account login website when I try browsing. I tethered on a train ride last weekend and had to swap my SIM over to my Note 1 for tethering. Is this due to the IPv4/IPv6 issue? I have the Note 1 set to IPv4 because the CM10.2 ROM crashed on IPv6 randomly.
Samsung Galaxy Note 3 SM-900T 32GB
Samsung Galaxy Note SGH-i717 16GB
HP TouchPad 32GB
Archos 43 Internet Tablet - 16GB + 32GB mSD
Dell Axim X50v - 128MB + 16GB CF