I too will be in BCN for a couple days early May. I have a usa unlocked Samsung s7 edge on the TMO network. Since I am on tmo and there is unltd data for outside the usa, I think i'll be ok - although I may be limited to 3g speeds.

I also had a usa based tmo phone when I was in Tokyo/Manila some 2 yrs ago...and with tmo I had no problems w/connectivity....except that manila was quite spotty to get full bars on 3g.

Following this thread.