Access to USA mobile network from euro phone

I'm currently in the US with a cheap Archos 50d Oxygen phone. I cannot get voice nor data access. I have a french plan on Free (yeah, that's the name, and no, it's not free) which normally allows for foreign use (I've used it all over Europe, and they explicitly list the US as an allowed country). I bought this phone thinking it would work in the US because its frequencies are: GSM 1800, GSM 1900, GSM 850, GSM 900, LTE 1800, LTE 2600, LTE 800, WCDMA 2100, WCDMA 900. And for data: 2G - EDGE, 2G - GPRS, 2G - GSM, 3G - W-CDMA, 4G - LTE

Now, should it work in the US or am I mistaken about the frequencies ?

When I do a network search, the only one I can find (in California) if T-Mobile 2G, but it won't let me latch onto it. Yes, I have roaming enabled.

Any advice ?