Yes. There is NOTHING in the EM+ plan that says it's ok to use your data plan with anything other than the device that has your plan's SIM card inserted into it. Nor does it say anything specifically to contradict/set-aside/exempt the T&C/TOS explicit statement about tethering.

And, the T&C/TOS, still clearly state:

Your Data Plan is intended for Web browsing, messaging, and similar activities on your device and not on any other equipment. Unless explicitly permitted by your Data Plan, other uses, including for example, tethering your device to a personal computer or other hardware, are not permitted.


The only wiggle room is: whether or not you could get a lawyer to make it stick, in court, that "on your device" doesn't specify "on your directly serviced by T-Mobile, with your T-Mobile SIM card inserted into it, device". It's POSSIBLE to make that stick, but I'm willing to bet on T-Mobile's lawyers in that one. The spirit of it is clearly aimed against tethering, as explained just one sentence later.