Not at this time. Even though I bought it outright the only data plan available is the AT&T postpaid plan.

Its a standard micro SIM but when AT&T activates it they put it on a data device plan. Swapping the SIM out into a phone or vice-versa probably won't work because of the service activated on the SIM even though the SIM will fit.

Possibly. A lot will depend on the local towers you would be connected to. While the Mobley uses LTE it only uses one channel at a time, and depending on your region's towers those channels/towers could be slow if congested. Newer stand-alone WiFi hotspot devices are able to use two different channels at the same time to greatly improve throughput and help if one channel is busy. Newer devices also are likely to have more channel frequencies they can use. That said, no other WiFi hotspot can be set up for $20 unlimited data/month. We used our Mobley on a recent road trip with multiple kids streaming while going down the highway. Video can buffer for when you'd transition towers and video doesn't care much if you have a bad ping speed. So while your XBox would likely connect well, latency would potentially make multi-player gaming difficult.