We have to first split whats real 4G (LTE) data and whats 3G Hspa+/Faux 4G data.
4G LTE is a newer faster data technology, and it seems like only official T-mobile branded phones and expensive AT&T models with the exception of Pantech phones has this set of LTE Radios.
HSPA+ is based off older 3G technology. T-mobile found that they could enhance its 3G network at a time when the very first 4G Lte speed options were very slow in comparison. So impressive was HSPA+ speeds that T-mobile just called it 4G, Over time true 4G LTE matured and speeds blossomed. and confusion then ruled the mobile land.
As of the date of my post Blu does not have a single phone that supports T-mobile 4G LTE data.
But many of Blu's high end model Smartphones have 1900Mhz 3G/HSPA+ Radios running over T-mobiles re-farmed network.
Your issue would be finding out if your area got the re-farmed update.
(P.S. Good luck getting anyone from T-Mobile to properly help you.)
Here is what can help:
Part 1: You have to get a Blu model with an "A" or "U"( for example Blu Life Pure model L240a). The "a" in the model stand for America , Or "U" For United States and both has all the Proper radios to work on a Re-farmed T-Mobile network.
( NOTE: The "i" Or "L" on Blu phone models for example "Blu Life Pure L240i model" , The "i"standing for International. "L" For latin america?)
Part 2 What is a Re-farmed T-mobile market? Re-farmed simply means that t-mobile has shifted around its 2G, 3G/Faux4G data to its 1900 Radio band. If you have the correct BLU model (with the"u" "a") phone that supports the 1900 band and you live in a re farmed market you will be blessed with speeds on average of 1-7 MB down with people reporting higher after rooting and modding.
I can't tell you if your area has been re-farmed / or updated. You may have to check forums like Google plus community for more info:
I made a video regarding Blu Products telephones running data on T-mobile refarmed networks proving that its possible.
I made other videos regarding Blu products as well.
Just look for my videos on YouTube by searching"pdxrelentless blu studio 5.5" Or clicking the link above.
Anybody reading this is welcome to head over and review my Studio 5.5 you tube videos and in QA public discussions made on there.
Hope this helps you out.