For those of you with Galaxy S10's #DATA## passcode 000000 --> LTE --> and disable LTE bands 25, 26, and 41 and you will connect to Tmobiles network. I have been hanging out on it all day connected to B2, B12, B66, and even found 600MHz out in the wild. I must say locating Tmobile sites is difficult PCIs are all over the place and not sure how their GCIs correlate to each sector. Their network is dense AF here which makes it harder to pinpoint their sites.
Also speeds are still capped to 5mbps but found some neat configurations such as B2+B12 15+5MHz CA