What 3 states were you visiting? If you take the talk portion out of the equation (as this is the only feature affected by the decommissioning of the 3G network in the US) how was your texting and data services? T-Mobile offers excellent coverage in urban areas however their coverage in rural areas can be spotty and is reflected in their nationwide coverage of 62% just behind At&t's 68% national coverage (who it appears is no longer pm's roaming partner?). Voice services are currently provided on T-Mobile's 2G network where available.
Federal regulators in the US do not require the same kind of coverage as the CRTC mandates for Canadian network providers so you will find a significant difference in coverage depending on where you are traveling. Public mobile can offer you roaming services but they are limited to the coverage that their roaming partners offer their own customers. While you can ask for a credit for the talk portion of your roaming add ons don't expect a credit for the data and text portions just because you were unable to connect to the 4G LTE network in areas where it simply does not exist. One of the reasons the big three in Canada like to claim we have to pay so much more for our mobile services is because they boast that Canada has the best nation wide coverage and data speeds in the world. Customers roaming outside of Canada have to temper their mobile service expectations as they do not measure up to the mobile service they recieve at home.
Here's T-Mobile's coverage map....
