I don't know if this has been mentioned and corrected in the thread from what is written in the wiki (or perhaps T-Mobile modified their plans), but the 256kbps speed is available with their base T-Mobile One plan (no Plus add-on required). I asked 3 different reps to be sure. The Plus and Plus International add-ons supposedly give you additional hotspot and some other benefits, but all get the 256kbps roaming speed where available.