Install "Network cell info Lite", it'll show you what bands/connections are providing which service(s). It's limited to one main and a 2nd neighbor cell on the free version, but it's still VERY handy for stuff like this.
DON'T let it run in the background though, it'll eat up your battery ultra-fast, or at least it used to (the first thing I do when using it on new installs is disable any background processing).