If you're using the device for travel why would you buy something locked to your local provider? You may as well use your smartphone as a WiFi and incur any roaming charges T-Mobile want to screw you with.
If you want a mobile WiFi device (MiFi) for travel I suggest you get an unlocked item. (I've had a couple Huawei unlocked MiFi's and consider them fast and reliable with good battery life). Pop in a local prepaid SIM and you can run several devices off it without running down your phone battery.